Question

using the formula cos 2theta = 1 - 2 sin ^2 theta, find the value of sin 30, if cos 60 = 1/2

Answer 1

cos60° = 1 - 2sin^2 30° = 1/2
2 - 4sin^2 30° = 1 => 4sin^2 30° = 1 => sin^2 30° = 1/4 => sin30° = 1/2 (+ve for 1st quadrant)

Answer 2

Answer:1/2

Step-by-step explanation:

Cos2x=1-2sin^2x

Let x=30

Cos 2×30 =1-2sin^2(30)

Cos60=1-2sin^2(30)

1/2=1-2sin^2(30)

2sin^2(30)=1-1/2=1/2

sin^2(30)=1/4

sin30=√1/4

Sin30= 1/2