Question

Find cos ( 2 θ ) if sin ( θ ) = 2 /7

Answer 1

Answer:

Step-by-step explanation:

[Cos^2#-sin^2@]= 1-2sin^2@=1-2×4/49

=1- (8/49)

=(49-8)/49

=41/49

Answer 2

Answer:

sinA=2/7

cosA=√(1-sin²A) =√(1-4/49) =√45/7=3√5/7

sin2A=2sinA.cosA=2×2/7×3√5/7 =12√5/49

cos2A=√(1-sin²2A) =√(1- 720/2401)=√1681/49=41/49