Question

Since BC is parallel to DE, triangles ABC and ADE are similar. What are the lengths of the unknown sides?

A. AC = 14 cm; CE = 8 cm
B. AC = 12 cm; CE = 7 cm
C. AC = 10 cm; CE = 5 cm
D. AC = 5 cm; CE = 10 cm

Answer 1

C

Explanation:

Step 1: find BC

Given Triangles ABC and ADE are similar,

`(AB)/(AD)` =
`(BC)/(DE)`

BC =
`(AB)/(AD)` x DE

=
`(8)/(8 + 4)` x 9

= 6 cm

Step 2: use Pythagorean theorem to find AC and / or AE

Consider triangle ABC,

by Pythagorean theorem,

AB² + BC² = AC²

AC² = 6² + 8² = 100

AC = √100 = 10 (answer... we can see that C is the only one with AC=10.

Step 3: Verify.. even though we know that it is C because AC = 10, you can verify that the ansewer is correct by finding CE and confirming that CE=5

By using similar triangles ABC and ADE,

AC/AE = AB / AD

AE = AD/AB x AC = 12/8 x 10 = 15

CE = AE - AC = 15 - 10 = 5 (answer confirmed)