find the approximate values of cos 61 ° , it being given that sin 60 ° = 0.86603 and 1 ° = 0.01745 radian

Question

Philoid · Accepted Answer

Let y = cosx

Let x =60° and Δx = 1° .

As y =cos x

⇒

We, know

⇒

∴

⇒

∴ Δy = 0.01511

Also,

Δy = f(x+Δx)-f(x)

∴ 0.01511 = cos(60+1) – cos(60)

⇒ 0.01511 = cos61° – 0.5

⇒ cos61° = 0.48489