1.

If sinx = 2/3, then find the value of cos3x.1. -0.57972. 0.56783. 0.67354. -0.8765

Answer» Correct Answer - Option 1 : -0.5797

Given-

sinx = 2/3

Formula Used- 

cosx = √(1 - sin2x)

cos3x = 4cos3x - 3cosx  

Calculation - 

cosx = √(1 - 4/9)

⇒ √(5/9)

⇒ √5/3

cos3x = 4 × (√5/3)3 - 3 × √5/3

⇒ cos3x = 20√5/27 - √5

⇒ cos3x = -7√5/27

∴ cos3x = -0.5797



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