Question

In Fig. 5.47, the value of cos ϕ is
A. 5/4
B. 5/3
C. 3/5
D. 4/5

Answer 1

I think this should be the answer

Answer 2

D. 4/5

Step-by-step explanation:

We know that the sum of all the angles on one side of a straight line is 180°. These angles are said to be in linear pair.

Therefore, using the figure, we get

θ + ϕ + 90° = 180°

Therefore, θ = 90° - ϕ ------(1)

In ΔABC, sin θ = 4/5 ----- (2)

From (1) and (2), we get:

Sin(90°- ϕ) = 4/5

Cos ϕ = 4/5

Option D is the answer.