Q6 of 268 Page 5

If sin 77° = x, then write the value of cos 77o in terms of x.

We know that

cos2 θ + sin2 θ = 1


⇒ cos2 77° + sin2 77° = 1


⇒ cos 2 77° = 1 – sin2 77°


⇒ cos 77° = √(1 – sin2 77°)


And Given that sin 77° = x


⇒ cos 77° = √(1 – x2 )


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