if sin A = 3/8 , what is the value of cos 2A?

Question

help please

Answer 1

cos2A = 1 - 2sin²A  (double angle identity)

 

 

So, if sinA = 3/8, then cos2A = 1 - 2(3/8)² = 1 - 9/32 = 23/32

Answer 2

Use the double-angle identity for cos(2A), which is

 

cos²A - sin²A =

 

 

(1 - sin²A) - sin²A =

 

1 - 2sin²A

 

 

    or the equivalent

 

 

cos²A - (1 - cos²A) =

 

2cos²A - 1

 

 

Since we have sine, we want to use the first version of the double-angle identity.

 

1 - 2sin²A =

 

1 - 2(3/8)² =

 

1 - 2(9/64) =

 

1 - (9/32) =

 

23/32

Answer 3

x = cos (2A)

 

A= csc(3/8) ; csc = 1/sin(p), in this case p = 3/8

 

x= cos(2*csc(3/8))

 

Whoops, Mark is right.