Question

I don't understand?

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Answer 1

see explanation

Explanation:

The perimeter (P) is the length of all 3 sides of the triangle

The triangle is isosceles with 2 equal sides 20 - 7xy

P = 20 - 7xy + 20 - 7xy + 12 = 52 - 14xy

When x = 2, y = 1, then

P = 52 - 14(2)(1) = 52 - 28 = 24