Question 163877
Although you specified the book, chapter, and problem, we do not have access to your book.  
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Write back with the problem and I'll be glad to help you out.
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{{{ ((x^2+7x+12)/(x^2+3x+2))*((x^2+5x+6)/(x^2+6x+9))}}}
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First thing you do, is to factor...
{{{ (((x+4)(x+3))/((x+2)(x+1)))*(((x+2)(x+3))/((x+3)(x+3)))}}}
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Now, you can start "canceling" like-terms:
{{{ (((x+4)(x+3))/((x+2)(x+1)))*(((x+2))/((x+3)))}}}
{{{ ((x+4)(x+3)(x+2))/((x+2)(x+1)(x+3))}}}
{{{ ((x+4)(x+2))/((x+2)(x+1))}}}
{{{ ((x+4))/((x+1))}}}