Question

Find all possible solutions for x such that ∆ABC is congruent to ∆DEF.

∆ABC: sides length 7, 9, x

∆DEF: sides length 7, 10, x-1

The solution to x = _______.

Answer 1

9 doesn't equal 7
9 doesn't equal 10
so 9 equals... ?

Answer 2

Lengths of corresponding sides of congruent triangles are congruent.

9 would have to equal x-1

x would have to match to 10.