Forum - Trigonometry

Trigonometry identity

Johann
Visitor
2016-04-30 07:11:45
#1
Hi,
I need some help with this exercicse:
sin2 (a + b) = cos2a + cos2b - 2cos(a)cos(b)cos(a + b)
I have to show that this is true.

 

RE: Trigonometry identity

SteveC
Member
2016-04-30 07:16:13
#2
So, you have this
sin2 (a + b) = cos2a + cos2b - 2cos(a)cos(b)cos(a + b)


We have to use this formula

formula cosinus, trigonometry


I'm gonna start with the member from the right. So though, we have:


trigonometry, cosinus de b sinus de a


cosinus, trigonometrie
And then we know the formula: sin2 a + cos2a = 1 => cos2 a = 1 - sin2a


and we have
trigonometry, sin angles summary


trigonometry

 
 

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