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If theta=30 , cos3 theta=4cose^2 theta-3costheta, sin3 theta=3sin theta-4sin^3 theta​

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priya162

priya162

05.06.2017

Math

Secondary School

answered • expert verified

if theta =30° verify the following :- (a) cos 3 theta° = 4 cos ^3 theta - 3 cos theta (B) sin 3 theta° = 3 sin theta - 4 sin ^3 theta

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RaunakRaj

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a) cos(3×30°)=4cos^3(30°)-3cos(30°)

cos 90°=4cos^3(30°)-3cos(30°)

0=4(_/3÷2)^3-3×_/3÷2

0=(12_/3)/8-(3_/3)/2

0=(3_/3)/2-(3_/3)/2

0=0

b) sin(3×30°)=3sin(30°)-4sin^3(30°)

1=3×1/2 - 4×1/8

1=3/2-1/2

1=2/2

1=1

Hence all proved..