Question

If cos2x=cos60•cos30•+sin60•sin30, then find the value of x

Answer 1

2x = 60 -30
2x = 30
x = 15

because
Rhs = cos60•cos30•+sin60•sin30
= cos ( 60-30)

and Lhs = cos 2x

so we equate both the sides, we get
Cos 2x = Cos (60-30)
=> 2x = 60-30

Answer 2

Step-by-step explanation:

For class 10

cos2x = cos60×cos30 - sin60×sin30

cos2x = 1/2 × √3/2 - √3/2 × 1/2

cos2x = √3/4 - √3/4

cos2x  = 0

cos2x = cos90    {cos 90 = 0}

2x = 90

x = 90/2 = 45

For class 11 and above

cos2x = cos60 ×  cos30 - sin60 × sin30

cos2x = cos(60+30)

cos2x = cos90

2x = 90

x = 90/2 = 45

Hope it helps!!!

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