# Trig identity (hard)

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#1
Prove

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6 years ago
#2
(Original post by ubisoft)
Prove

Just use harmonic form

Cos(y) - Sin(y) = R Cos(y+a)

R will be

a will be
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#3
(Original post by TenOfThem)
Just use harmonic form
Haven't done that yet as I'm still on C3...

EDIT: how do you work out R and a?
0
6 years ago
#4
(Original post by ubisoft)
Haven't done that yet as I'm still on C3...

EDIT: how do you work out R and a?
Ok

So Cos(A+B) where B =
0
6 years ago
#5
math is sexy!
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#6
(Original post by TenOfThem)
Ok

So Cos(A+B) where B =
So then do you use the double angle properties to split it up?
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6 years ago
#7
(Original post by ubisoft)
So then do you use the double angle properties to split it up?
The compound angle rules, yes
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#8
(Original post by TenOfThem)
The compound angle rules, yes
Thanks, I've done it now. It was from a proof by induction question from FP2, I had to look up the harmonic form thing and it became clear.
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