B
B
17
8
A
15
C
Find cos(B) in the triangle.

25

Step-by-step explanation:

Angle ADB is the same as Angle CBD because alternate angles are always equal to each other.

Angle ADB + Angle CDB = 90 because Angle ADC is a right angle.

So if we substitute in..

7k + 60 +(-5k +40) = 90

2k + 100 = 90

2k = - 10

k = - 5

Now because Angle CBD is equal to Angle ADB, all we have to do is work out Angle ADB to get the answer

Sub in our k value..

Angle CBD = 7(-5) + 60 = 25