6.1: Exponents rules and properties
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If a is a positive real number and n is any real number, then in an, a is called the base and n is called the exponent.
When the directions state simplify, this means
- All exponents are positive
- Each base only occurs once
- There are no parenthesis
- There are no powers written to powers
Product Rule of Exponents
Let’s take a look at an example with multiplication.
Simplify: a3⋅a2
Solution
First, let’s rewrite this product in expanded form and then combine with one base a.
a3⋅a2Expand(a⋅a⋅a)⋅(a⋅a)Rewrite with one base aa⋅a⋅a⋅a⋅a⏟5 timesMultiplying a five timesa5Simplified expression
Let’s think about Example 6.1.1 . This method of expanding seems to be fine when there are smaller exponents, but what if we were given something like a100⋅a934? Are we going to expand a over a thousand times? No way! We need a more sophisticated way in multiplying expressions with exponents. Hence, taking a look at Example 6.1.1 , we can see the result is a5. Notice we could have obtained this answer without expanding but by simply adding the exponents:
a3⋅a2=a3+2=a5
This is called the product rule of exponents.
Let a be a positive real number and n and m be any real number. Then an⋅am=an+m
In order to add exponents, the bases of the factors are required to be the same.
Simplify: 32⋅36⋅3
Solution
Let’s apply the product rule and simplify. Don’t forget that 3 has an exponent, it is one: 31.
We don’t always write it, but we know it’s there.
32⋅36⋅31Same base32+6+1Add the exponents39Simplified expression
We can simplify this even more as 19,683 (39=19683).
Simplify: (2x3y5z)⋅(5xy2z3)
Solution
(2x3y5z)⋅(5xy2z3)Rewrite without parenthesis2x3y5z1⋅5x1y2z3Multiply the coefficients and add exponents with same bases2⋅5⋅x3+1⋅y5+2⋅z1+3Add exponents and multiply the coefficients10x4y7z4Simplified expression
Quotient Rule of Exponents
Simplify: a5a2
Solution
a5a2Expanda⋅a⋅a⋅a⋅aa⋅aReduce the common factorsa⋅a⋅a⋅a⋅aa⋅aSimplifya⋅a⋅aRewrite with one base aa3Simplified expression
Let’s think about Example 6.1.4 . This method of expanding seems to be fine when there are smaller exponents, but what if we were given something like a199a827? Are we going to expand a over a thousand times? No way! We need a more sophisticated way in dividing expressions with exponents. Hence, taking a look at Example 6.1.4 , we can see the result is a3. Notice we could have obtained this answer without expanding but by simply subtracting the exponents:
a5a2=a5−2=a3
This is called the quotient rule of exponents.
Let a be a positive real number and n and m be any real number. Then anam=an−m
In order to subtract exponents, the bases of the dividend and divisor are required to be the same. Be sure that the denominator exponent is subtracted from the numerator exponent.
Simplify: 71375
Solution
71375Same base713−5Subtract exponents78Simplified expression
We can simplify this even more as 5,764,801 (78=5764801).
Simplify: 5a3b5c22ab3c
Solution
5a3b5c22a1b3c1Subtract exponents with same bases and simplify coefficients, if possible5a3−1b5−3c2−12Simplify5a2b2c2Simplified expression
We could also write the expression with the fraction as a coefficient: 52a2b2c. These are equivalent and both correct.
Power Rule of Exponents
Simplify: (a2)3
Solution
First, let’s rewrite this expression in expanded form and then combine with one base a.
(a2)3Expanda2⋅a2⋅a2Apply the product rulea2+2+2Add exponentsa6Simplified expression
Let’s think about Example 6.1.7 . This method of expanding seems to be fine when there are smaller exponents, but what if we were given something like (a760)34? Are we going to expand a over a twenty-thousand times? No way! We need a more sophisticated way in simplifying expressions with exponents raised to exponents. Hence, taking a look at Example 6.1.7 , we can see the result is a6. Notice we could have obtained this answer without expanding but by simply multiplying the exponents:
(a2)3=a2⋅3=a6
This is called the power rule of exponents.
Let a be a positive real number and n and m be any real number. Then (an)m=am⋅n
Furthermore, we can extend the power rule for when we have more than one factor in the base.
Simplify: (ab)3
Solution
We can expand the base, then rewrite with one base of a and b.
(ab)3Expand(ab)(ab)(ab)Let's rewrite this grouping a's and b'sa⋅a⋅a⋅b⋅b⋅bRewrite with one base of a and ba3b3Simplified expression
Let’s think about Example 6.1.8 . This method of expanding seems to be fine when there are smaller exponents, but what if we were given something like (ab)2049? Are we going to expand a and b over a two-thousand times? No way! We need a more sophisticated way in simplifying expressions with exponents raised to exponents with more than one factor in the base. Hence, taking a look at Example 6.1.8 , we can see the result is a3b3. Notice we could have obtained this answer without expanding but by simply applying the exponent to each factor in the base:
(ab)3=a3⋅b3=a3b3
This is called the power of a product rule (POP).
Let a and b be a positive real numbers and n be any real number. Then (ab)n=an⋅bm
It is important to be careful to only use the power of a product rule with multiplication inside parenthesis. This property is not allowed for addition or subtraction, i.e., (a+b)m≠am+bm
Simplify: (ab)3
Solution
Let’s expand the fraction and rewrite with one base of a and b.
(ab)3Expand(ab)(ab)(ab)Multiply fractionsa3b3Simplified expression
Notice, this is similar to the POP rule and we can apply the exponent to each numerator and denominator.
Let a and b be a positive real numbers and n be any real number. Then (ab)n=anbn
Let’s look at an example where we have to combine all these exponent rules.
Simplify: (x3yz2)4
Solution
(x3y1z2)4Apply the POP rulex3⋅4y1⋅4z2⋅4Multiply exponentsx12y4z8Simplified expression
Simplify: (a3bc8d5)2
Solution
(a3b1c8d5)2Apply the power of a quotient rulea3⋅2b1⋅2c8⋅2d5⋅2Multiply exponentsa6b2c16d10Simplified expression
Simplify: (4x2y5)3
Solution
(41x2y5)3Apply the POP rule43⋅1x2⋅3y5⋅3Multiply exponents43⋅x6⋅y15Evaluate 4364x6y15Simplified expression
Notice that the exponent also applied to the coefficient 4 and we had to evaluate 43=64 as part of the expression.
Let a and b be positive real numbers and n and m be any real numbers.
Rule 1. an⋅am=an+m
Rule 2. anam=an−m
Rule 3. (an)m=anm
Rule 4. (ab)n=an⋅bn
Rule 5. (ab)n=anbn
Zero as an Exponent
Here we discuss zero as an exponent. This is one of two cases where the exponent isn’t positive. The other case is where the exponents are negative, but we will save that for the next section. Let’s look an example:
Simplify: a3a3
Solution
If we applied the quotient rule right away, we would get
a3a3=a3−3=a0
But what does this mean? What is a0? Well, let’s take a look at this same example with a different approach:
a3a3Expanda⋅a⋅aa⋅a⋅aReduce common factors of aa⋅a⋅aa⋅a⋅aSimplify11Simplify1Simplified expression
If a3a3=a0 from the first part and a3a3=1 from the second part, then this implies a0=1.
Let a be a positive real number. Then a0=1, i.e., any positive real number to the power of zero is 1.
Simplify: (3x2)0
Solution
Since 3x2 is raised to the power of zero, then we can apply the zero power rule:
(3x2)0Zero power rule1Simplified expression
Negative Exponents
Another property we consider is expressions with negative exponents.
Simplify: a3a5
Solution
If we applied the quotient rule right away, we would get
a3a5=a3−5=a−2
But what does this mean? What is a−2? Well, let’s take a look at this same example with a different approach:
a3a5Expanda⋅a⋅aa⋅a⋅a⋅a⋅aReduce common factors of aa⋅a⋅aa⋅a⋅a⋅a⋅aSimplify1a⋅aSimplify1a2Simplified expession
If a3a5=a−2 from the first part and a3a5=1a2 from the second part, then this implies a−2=1a2.
This example illustrates an important property of exponents. Negative exponents yield the reciprocal of the base. Once we take the reciprocal, the exponent is now positive.
It is important to note a negative exponent does not imply the expression is negative, only the reciprocal of the base. Hence, negative exponents imply reciprocals.
Also, recall the rules of simplifying:
- All exponents are positive
- Each base only occurs once
- There are no parenthesis
- There are no powers written to powers
This includes rewriting all negative exponents as positive exponents.
Let a and b be positive real numbers and n be any real number.
Rule 1. a−n=1an
Rule 2. 1a−n=an
Rule 3. (ab)−n=(ba)n
Negative exponents are combined in several different ways. As a general rule, in a fraction, a base with a negative exponent moves to the other side of the fraction bar as the exponent changes sign.
Simplify: a3b−2c2d−1e−4f2
Solution
We can rewrite the expression with positive exponents using the rules of exponents:
a3b−2c2d−1e−4f2Reciprocate the terms with negative exponentsa3cde42b2f2Simplified expression
As we simplified the fraction, we took special care to move each base that had a negative exponent, but the expression itself did not become negative. Also, it is important to remember that exponents only effect the base. The 2 in the denominator has an exponent of one (we don’t always write it, but we know it’s there), so it does not move with the d.
Nicolas Chuquet, the French mathematician of the 15th century wrote 121¯m to indicate 12x−1. This was the first known use of the negative exponent.
Properties of Exponents
Putting all the rules together, we can simplify more complex expression containing exponents. Here we apply all the rules of exponents to simplify expressions.
Let a and b be positive real numbers and n and m be any real numbers.
Rule 1. an⋅am=an+m
Rule 2. anam=an−m
Rule 3. (an)m=anm
Rule 4. (ab)n=an⋅bn
Rule 5. (ab)n=anbn
Rule 6. a0=1
Rule 7. a−n=1an
Rule 8. 1a−n=an
Rule 9. (ab)−n=(ba)n
Simplify: 4x−5y−3⋅3x3y−26x−5y3
Solution
4x−5y−3⋅3x3y−26x−5y3Simplify the numerator by applying the product rule12x−2y−56x−5y3Simplify by applying the quotient rule126⋅x−2−(−5)y−5−3Simplify2x3y−8Rewrite with only positive exponents2x3y8Simplified expression
Simplify: (3ab3)−2⋅ab−32a−4b0
Solution
(3ab3)−2⋅a1b−32a−4b0Apply POP and zero power rule3−2a−2b−6⋅a1b−32a−4⋅1Apply product rule3−2a−1b−92a−4Apply the quotient rule3−2a3b−92Rewrite with only positive exponentsa32⋅32⋅b9Simplifya318b9Simplified expression
It is important to point out that when we simplified 3−2, we moved the 3−2 to the denominator and the exponent became positive. We did not make the number negative. Negative exponents never make the bases negative; they simply mean we have to take the reciprocal of the base.
Simplify: (3x−2y5z3⋅6x−6y−2z−39(x2y−2)−3)−3
Solution
This example looks more involved that any of the other examples, but we will apply the same method. It is advised, in these types of problems, that we simplify the expression inside the parenthesis first, and then apply the POP rule. We even should start with simplifying each numerator and denoinator before simplifying the fraction with the quotient rule.
(3x−2y5z3⋅6x−6y−2z−39(x2y−2)−3)−3Simplify each numeratr and denominator(18x−8y3z09x−6y6)−3Apply the quotient rule(2x−2y−3z0)−3Apply the POP rule2−3x−6y9z0Rewrite only with positive exponentsx6y923Simplifyx6y98Simplified expression
Exponent Rules and Properties Homework
Simplify. Be sure to follow the simplifying rules and write answers with positive exponents.
4⋅44⋅44
4⋅22
3m⋅3mn
2m4n2⋅4nm2
(33)4
(44)2
(2u3v2)2
(2a4)4
4543
323
3nm23n
4x3y43xy3
(x3y4⋅2x2y3)2
2x(x4y4)4
2x7y53x3y⋅4x2y3
((2x)3x3)2
(2y17(2x2y4)4)3
(2mn4⋅2m4n4mn4)3
2xy5⋅2x2y32xy4⋅y3
q3r2⋅(2p2q2r3)22p3
(zy3⋅z3x4y4x3y3z3)4
2x2y2z6⋅2zx2y2(x2z3)2
4⋅44⋅42
3⋅33⋅32
3x⋅4x2
x2y4⋅xy2
(43)4
(32)3
(xy)3
(2xy)4
3733
343
x2y44xy
xy34xy
(u2v2⋅2u4)3
3vu5⋅2v3uv2⋅2u3v
2ba7⋅2b4ba2⋅3a3b4
2a2b2a7(ba4)2
yx2⋅(y4)22y4
n3(n4)22mn
(2y3x2)22x2y4⋅x2
2x4y5⋅2z10x2y7(xy2z2)4
(2q3p3r4⋅2p3(qrp3)2)4
2x4y−2⋅(2xy3)4
(a4b−3)3⋅2a3b−2
(2x2y2)4x−4
(x3y4)3⋅x−4y4
2x−3y23x−3y3⋅3x0
4xy−3⋅x−4y04y−1
u2v−12u0v4⋅2uv
u24u0v3⋅3v2
2y(x0y2)4
(2a2b3a−1)4
2nm4(2m2n2)4
(2mn)4m0n−2
y3⋅x−3y2(x4y2)3
2u−2v3⋅(2uv4)−12u−4v0
(2x0⋅y4y4)3
y(2x4y2)22x4y0
2yzx22x4y4z−2⋅(zy2)4
2kh0⋅2h−3k0(2kj3)2
(cb3)2⋅2a−3b2(a3b−2c3)3
(yx−4z2)−1z3⋅x2y3z−1
2a−2b−3⋅(2a0b4)4
2x3y2⋅(2x3)0
(m0n3⋅2m−3n−3)0
2m−1n−3⋅(2m−1n−3)4
3y33yx3⋅2x4y−3
3x3y24y−2⋅3x−2y−4
2xy2⋅4x3y−44x−4y−4⋅4x
2x−2y24yx2
(a4)42b
(2y−4x2)−2
2y2(x4y0)−4
2x−3(x4y−3)−1
2x−2y0⋅2xy4(xy0)−1
2yx2⋅x−2(2x0y4)−1
u−3v−42v(2u−3v4)0
b−1(2a4b0)0⋅2a−3b2
2b4c−2⋅(2b3c2)−4a−2b4
((2x−3y0z−1)3⋅x−3y22x3)−2
2q4⋅m2p2q4(2m−4p2)3
2mpn−3(m0n−4p2)3⋅2n2p0