9514 1404 393
Answer:
the equation comes from setting expressions for the perimeters equal to each other
Explanation:
Each of the relations is described in terms of the shortest side of the triangle, which is what we're asked to find. It makes sense to let a variable represent that length.
shortest triangle side: s
each of the other two sides: s+1
perimeter of the triangles: s +(s+1) +(s+1) = 3s+2
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side length of square: s-2
perimeter of square : 4(s -2) = 4s -8
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The two perimeters are equal, so we have ...
3s +2 = 4s -8 . . . . . your equation
10 = s . . . . . . . . . . . add 8-3s