Question 70331
You multiply {{{(x^5)*(x^7)}}} by just adding the two exponents to get {{{x^12}}}.
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Think about it. By the definition of exponents:
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{{{x^5 = x*x*x*x*x}}} and
{{{x^7 = x*x*x*x*x*x*x}}}
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When you multiply the right sides of these two equations the problem becomes:
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{{{(x*x*x*x*x)*(x*x*x*x*x*x*x)}}}
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so you end up with 12 x's all multiplied together which is, by definition, {{{x^12}}}

Hope this helps you understand why the exponent is 12.