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avatar+91 

how does sin 4a equal to each of the following:

a) 2 sin 2a cos 2a

b)4 sin a cos a - 8 sin^3 a cos a

c) 4 sin a cos a cos 2a 

d) 4 sin a cos^3 a - 4 sin^3 a cos a

 

what are the rules that give you those longass equations from just sin 4a ???

 Nov 30, 2016

Best Answer 

 #1
avatar+129899 
+5

how does sin 4a equal to each of the following:

 

a) 2 sin 2a cos 2a

This is just based on the identity that sin2a  = 2sinacosa.......so ...sin 4a   = sin 2(2a)  = 2sin2acos2a

 

b)4 sin a cos a - 8 sin^3 a cos a

Factor out  4 sina cosa

4 sina cosa  [ 1 - 2sin^2A]    =  

2 [2sin a cos a]  [ cos 2a ] =

2 [sin2a] [cos 2a]  =

sin 4a

 

 

 

c) 4 sin a cos a cos 2a 

2 [2 sina cos a] cos2a  =

2 [sin 2a] [ cos 2a]  =

sin 4a

 

 

 

d) 4 sin a cos^3 a - 4 sin^3 a cos a

Factor out   4sinacosa  =

4 sina cosa [  cos^2 a - sin^2 a]   =

4sina cos a  [ cos2a] =

2 [2sina cos a ] [cos 2a] =

2 [sin2a] [cos 2a]  =

sin 4a

 

Metallica......looks like we can delay your execution for at least a couple of days.......or so......LOL!!!

 

 

 

cool cool cool

 Nov 30, 2016
 #1
avatar+129899 
+5
Best Answer

how does sin 4a equal to each of the following:

 

a) 2 sin 2a cos 2a

This is just based on the identity that sin2a  = 2sinacosa.......so ...sin 4a   = sin 2(2a)  = 2sin2acos2a

 

b)4 sin a cos a - 8 sin^3 a cos a

Factor out  4 sina cosa

4 sina cosa  [ 1 - 2sin^2A]    =  

2 [2sin a cos a]  [ cos 2a ] =

2 [sin2a] [cos 2a]  =

sin 4a

 

 

 

c) 4 sin a cos a cos 2a 

2 [2 sina cos a] cos2a  =

2 [sin 2a] [ cos 2a]  =

sin 4a

 

 

 

d) 4 sin a cos^3 a - 4 sin^3 a cos a

Factor out   4sinacosa  =

4 sina cosa [  cos^2 a - sin^2 a]   =

4sina cos a  [ cos2a] =

2 [2sina cos a ] [cos 2a] =

2 [sin2a] [cos 2a]  =

sin 4a

 

Metallica......looks like we can delay your execution for at least a couple of days.......or so......LOL!!!

 

 

 

cool cool cool

CPhill Nov 30, 2016
 #2
avatar+91 
0

LOL. Thanks for the help.

 Dec 1, 2016

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