Question

What is the value of sin 2A

Answer 1

FIRST YOU HAVE WRITTEN WRONG QUESTION BUT I GIVE YOU ONE EXAMPLE



If sin(A) = 4/5, then, by drawing a 3-4-5 triangle: 
cos(A) = ±3/5. 
(Pick the positive value if A lies in Quadrants I or IV; pick the negative value in Quadrants II and III.) 

Therefore, by the double-angle formula for sine: 
sin(2A) = 2sin(A)cos(A) 
= 2(4/5)(±3/5) 
= ±24/25

Answer 2

Sin 2A  = 2 Sin A  cos A

this is the formula