In the construction of a segment congruent to a given segment shown, what is cd?

If segments AB and CD are congruent, then they have equal lengths:

5x-2=2x+7.

Solve this equation.

1. Separate terms with x and without x in different sides:

5x-2x=7+2,

3x=9.

2. Divide by 3:

x=3.

Then CD=2x+7=2·3+7=6+7=13.

correct choice is B.

where's the diagrams?

because linear equations are a lot simpler than quadratics equations, and linear equations formula is a lot easier to memorize. that's why i think they're harder.