Fun with Exponents!

Algebra Level 2

If a b = 2 a-b=2 and x a 2 x b 2 = x 32 \dfrac{x^{a^{2}}}{x^{b^{2}}}=x^{32} , then what is a b ab if a a and b b are positive integers?

80 48 99 63

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1 solution

Jordan Cahn
Oct 15, 2018

Using the properties of exponents, x a 2 x b 2 = x 32 x a 2 b 2 = x 32 a 2 b 2 = 32 ( a b ) ( a + b ) = 32 2 ( a + b ) = 32 a + b = 16 \begin{aligned} \frac{x^{a^2}}{x^{b^2}} &= x^{32} \\ x^{a^2-b^2}&= x^{32} \\ a^2-b^2 &= 32 \\ (a-b)(a+b) &= 32 \\ 2(a+b) &= 32 \\ a+b &= 16 \end{aligned}

Since a b = 2 a-b=2 and a + b = 16 a+b = 16 , the values of a a and b b are 9 9 and 7 7 , respectively. Thus a b = 63 ab=\boxed{63} .

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