Question

Find x.

A) 2√5

B) 3√5

C) 6

Answer 1

Look at the picture.

ΔABC and ΔDAC are similar. Therefore the sides of the triangles are in proportion:

`(AC)/(BC)=(DC)/(AC)`

AC = x

BC = 5 + 4 = 9

DC = 4

Substitute:

`(x)/(9)=(4)/(x)` cross multiply

`x^2=(9)(4)\\\\x^2=36\to x=√(36)\\\\\boxed{x=6\to C)}`