Question

if theta= 30° find the value of 3costheta - 4cosacubetheta​

Answer 1

Answer:

Step-by-step explanation:

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..

Actually it a trigonometric formula in class 11.