Give Me The rule of Math ab=?
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Basic rules for exponentiation
If n is a positive integer and x is any real number, then xn corresponds to repeated multiplicationxn=x×x×⋯×x⏟n times.We can call this “x raised to the power of n,” “x to the power of n,” or simply “x to the n.” Here, x is the base and n is the exponent or the power.
From this definition, we can deduce some basicrules that exponentiation must follow as well as some hand special cases that follow from the rules. In the process, we'll define exponentials xa for exponents a that aren't positive integers.
The rules and special cases are summarized in the following table. Below, we give details for each one.
Rule or special caseFormulaExampleProductxaxb=xa+b2223=25=32Quotientxaxb=xa−b2322=21=2Power of power(xa)b=xab(23)2=26=64Power of a product(xy)a=xaya36=62=(2⋅3)2=22⋅32=4⋅9=36Power of onex1=x21=2Power of zerox0=120=1Power of negative onex−1=1x2−1=12Change sign of exponentsx−a=1xa2−3=123=18Fractional exponentsxm/n=n√xm=(n√x)m43/2=(√4)3=23=8
The rules
Product of exponentials with same base
If we take the product of two exponentials with the same base, we simply add the exponents:xaxb=xa+b.
To see this rule, we just expand out what the exponents mean. Let's start out with a couple simple examples.3432=(3×3×3×3)×(3×3)=3×3×3×3×3×3=36y2y3=(y×y)×(y×y×y)=y×y×y×y×y=y5
The general case works the same way. We just need to keep track of the number of factors we have.xaxb=x×⋯×x⏟a times×x×⋯×x⏟b times=x×⋯×x⏟a+b times=xa+b
Quotient of exponentials with same base
If we take the quotient of two exponentials with the same base, we simply subtract the exponents:xaxb=xa−b
This rule results from canceling common factors in the numerator and denominator. For example:y5y3=y×y×y×y×yy×y×y=(y×y)×(y×y×y)y×y×y=y×y=y2.
To show this in general, we look at two different cases. If we imagine that a>b, then this rule follows from canceling the common b factors of xthat occur in both the numerator and denominator. We are left with just b−a factors of x in the numerator.xaxb=a times⏞x×⋯×xx×⋯×x⏟b times=a−b times⏞x×⋯×x×b times⏞x×⋯×xx×⋯×x⏟b times=x×⋯×x⏟a−b times=xa−b
If a<b, then what happens? We cancel all the x's from the numerator and are left with b−a of them in the denominator.xaxb=a times⏞x×⋯×xx×⋯×x⏟b times=a times⏞x×⋯×xx×⋯×x⏟b−a times×x×⋯×x⏟a times=1x×⋯×x⏟b−a timesTo make the above rule work for this case, we must define a negative exponent to mean a power in the denominator. If n is a positive integer, we definex−n=1x×x×⋯×x⏟n times.Then the rule for the quotient of exponentials works even if a<b:xaxb=x×⋯×x⏟a timesx×⋯×x⏟b times=1x×⋯×x⏟b−a times=xa−b.When b>a, the exponent a−b is a negative number. Since formula (2) is the same no matter the relationship between a and b, we don't need to worry about it and can just subtract the exponents.
Power of a power
We can raise exponential to another power, or take a power of a power. The result is a single exponential where the power is the product of the original exponents:(xa)b=xab.
We can see this result by writing it as a product where the xa is repeated b times:(xa)b=xa×xa×⋯×xa⏟b times.Next we apply rule (1) for the product of exponentials with the same base. We use this rule b times to conclude that(xa)b=xa×xa×⋯×xa⏟b times=xb times⏞a+a+⋯+a=xab.In the last step, we had to remember that multiplication can be defined as repeated addition.
Power of a product
If we take the power of a product, we can distribute the exponent over the different factors:(xy)a=xaya.
We can show this rule in the same way as we show that you can distribute multiplication over addition. One way to show this distributive law for multiplication is is to remember that multiplication is defined as repeated addition:(x+y)a=(x+y)+(x+y)+⋯+(x+y)⏟a times=x+x+⋯+x⏟a times+y+y+⋯+y⏟a times=xa+ya.In the same way, we can show the distributive law for exponentiation:(xy)a=(xy)×(xy)×⋯×(xy)⏟a times=x×x×⋯×x⏟a times×y×y×⋯×y⏟a times=xaya.
This rule also works for quotients(xy)a=xaya,but it does NOT work for sums. For example,(3+5)2=82=64,but this is NOT equal to32+52=9+25=34.
Special cases
The following are special cases that follow from the rules.
The power of one
The simplest special case is that raising any number to the power of 1 doesn't do anything:x1=x.
The power of zero
As long as x isn't zero, raising it to the power of zero must be 1:x0=1.
We can see this, for example, from the quotient rule, as1=xaxa=xa−a=x0.
The expression 00 is indeterminate. You can see that it must be indeterminate, because you can come up with good reasons for it to be two different values.
First, from above, if x≠0, then x0=1, no matter how small x is. If we just let x go all the way to zero (take the limit as x goes to zero), then it seems that 00 should be 1.
On the other hand, 0a=0 as long as a≠0. Repeated multiplication of 0 still gives zero, and we can use the above rules to show 0a still is zero, no matter how small a is, as long as it is nonzero.
If n is a positive integer and x is any real number, then xn corresponds to repeated multiplicationxn=x×x×⋯×x⏟n times.We can call this “x raised to the power of n,” “x to the power of n,” or simply “x to the n.” Here, x is the base and n is the exponent or the power.
From this definition, we can deduce some basicrules that exponentiation must follow as well as some hand special cases that follow from the rules. In the process, we'll define exponentials xa for exponents a that aren't positive integers.
The rules and special cases are summarized in the following table. Below, we give details for each one.
Rule or special caseFormulaExampleProductxaxb=xa+b2223=25=32Quotientxaxb=xa−b2322=21=2Power of power(xa)b=xab(23)2=26=64Power of a product(xy)a=xaya36=62=(2⋅3)2=22⋅32=4⋅9=36Power of onex1=x21=2Power of zerox0=120=1Power of negative onex−1=1x2−1=12Change sign of exponentsx−a=1xa2−3=123=18Fractional exponentsxm/n=n√xm=(n√x)m43/2=(√4)3=23=8
The rules
Product of exponentials with same base
If we take the product of two exponentials with the same base, we simply add the exponents:xaxb=xa+b.
To see this rule, we just expand out what the exponents mean. Let's start out with a couple simple examples.3432=(3×3×3×3)×(3×3)=3×3×3×3×3×3=36y2y3=(y×y)×(y×y×y)=y×y×y×y×y=y5
The general case works the same way. We just need to keep track of the number of factors we have.xaxb=x×⋯×x⏟a times×x×⋯×x⏟b times=x×⋯×x⏟a+b times=xa+b
Quotient of exponentials with same base
If we take the quotient of two exponentials with the same base, we simply subtract the exponents:xaxb=xa−b
This rule results from canceling common factors in the numerator and denominator. For example:y5y3=y×y×y×y×yy×y×y=(y×y)×(y×y×y)y×y×y=y×y=y2.
To show this in general, we look at two different cases. If we imagine that a>b, then this rule follows from canceling the common b factors of xthat occur in both the numerator and denominator. We are left with just b−a factors of x in the numerator.xaxb=a times⏞x×⋯×xx×⋯×x⏟b times=a−b times⏞x×⋯×x×b times⏞x×⋯×xx×⋯×x⏟b times=x×⋯×x⏟a−b times=xa−b
If a<b, then what happens? We cancel all the x's from the numerator and are left with b−a of them in the denominator.xaxb=a times⏞x×⋯×xx×⋯×x⏟b times=a times⏞x×⋯×xx×⋯×x⏟b−a times×x×⋯×x⏟a times=1x×⋯×x⏟b−a timesTo make the above rule work for this case, we must define a negative exponent to mean a power in the denominator. If n is a positive integer, we definex−n=1x×x×⋯×x⏟n times.Then the rule for the quotient of exponentials works even if a<b:xaxb=x×⋯×x⏟a timesx×⋯×x⏟b times=1x×⋯×x⏟b−a times=xa−b.When b>a, the exponent a−b is a negative number. Since formula (2) is the same no matter the relationship between a and b, we don't need to worry about it and can just subtract the exponents.
Power of a power
We can raise exponential to another power, or take a power of a power. The result is a single exponential where the power is the product of the original exponents:(xa)b=xab.
We can see this result by writing it as a product where the xa is repeated b times:(xa)b=xa×xa×⋯×xa⏟b times.Next we apply rule (1) for the product of exponentials with the same base. We use this rule b times to conclude that(xa)b=xa×xa×⋯×xa⏟b times=xb times⏞a+a+⋯+a=xab.In the last step, we had to remember that multiplication can be defined as repeated addition.
Power of a product
If we take the power of a product, we can distribute the exponent over the different factors:(xy)a=xaya.
We can show this rule in the same way as we show that you can distribute multiplication over addition. One way to show this distributive law for multiplication is is to remember that multiplication is defined as repeated addition:(x+y)a=(x+y)+(x+y)+⋯+(x+y)⏟a times=x+x+⋯+x⏟a times+y+y+⋯+y⏟a times=xa+ya.In the same way, we can show the distributive law for exponentiation:(xy)a=(xy)×(xy)×⋯×(xy)⏟a times=x×x×⋯×x⏟a times×y×y×⋯×y⏟a times=xaya.
This rule also works for quotients(xy)a=xaya,but it does NOT work for sums. For example,(3+5)2=82=64,but this is NOT equal to32+52=9+25=34.
Special cases
The following are special cases that follow from the rules.
The power of one
The simplest special case is that raising any number to the power of 1 doesn't do anything:x1=x.
The power of zero
As long as x isn't zero, raising it to the power of zero must be 1:x0=1.
We can see this, for example, from the quotient rule, as1=xaxa=xa−a=x0.
The expression 00 is indeterminate. You can see that it must be indeterminate, because you can come up with good reasons for it to be two different values.
First, from above, if x≠0, then x0=1, no matter how small x is. If we just let x go all the way to zero (take the limit as x goes to zero), then it seems that 00 should be 1.
On the other hand, 0a=0 as long as a≠0. Repeated multiplication of 0 still gives zero, and we can use the above rules to show 0a still is zero, no matter how small a is, as long as it is nonzero.
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Algebraic Terms 2a means 2 × a ab means a × b a means a × a a means a × a × a means a ÷ bmeans a × a × b ÷ c Adding a.
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