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Find the approximate value of cos (60° 30').

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Question

Find the approximate value of cos (60° 30').

(Given: 1° = 0.0175c, sin 60° = 0.8660)

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Solution

Let `f(X)=cosx`

`f'(x)=-sinx`

`x=60^@30'=60^@+(1/2)^@=a+h`

Here, `a=60^@=pi/3`

and `h=(1/2)^@=(0.0175)/2=0.00875`

`f(a)=f(pi/3)=cos(pi/3)=1/2=0.5`

`f'(a)=f'(pi/3)=-sin(pi/3)=-0.8660`

`f(a+h)~~f(a)+hf'(a)`

`cos(60^@30')~~0.5+(0.00875)(-0.8660)`

`~~0.5-0.0075775`

`~~0.4924`

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2016-2017 (July)

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