Question 71692
The perimeter of a geometric figure is defined as the sum of the lengths of all its sides.
You are given that the three sides of a triangle are 3x + 7, 4x - 9, and 5x + 6.  All you
need to do is to add up the expressions for the sides and the result will be the polynomial
that represents the perimeter.
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In equation form we can write this as:
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{{{P = 3x + 7 + 4x - 9 + 5x + 6}}}
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Where P represents the perimeter and x represents some unknown length.
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Add all the terms that contain an x on the right side.  You will add 3x + 4x + 5x and that
sum is 12x. Put it into the perimeter equation in place of the three terms that contained
an "x".  The equation becomes:
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{{{P = 12x + 7 - 9 + 6}}}
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Algebraically sum the three numbers on the right side. You will add +7 -9 and +6. The 
result you should get is +4. Substitute that into the equation in place of the 7, the -9,
and the +6.  The equation then is:
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{{{P = 12x + 4}}}.
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There it is ... the polynomial that represents the perimeter.
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Hope this helps you with your study of algebra and geometry.