Question

if sin2a=2sina*cosa
So, sin4a=?

Answer 1

Sin 2a=2sinacosa.
Sin 4a=sin 2.2a=2sin2acos2a=4sinacosacos2a by expanding sin2a again in last step

Answer 2

hey there,
   sin2a =2sina*cosa 

then sin4a = 2 sin2a*cos2a
  => 2*2sina*cosa*(cos²a-sin²a)
 => 4sina*cos³a - 4sin³a*cosa            
    
because cos2a = cos²a -sin²a 


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