If sin(x+y)=a and sin(x+z)=b , then prove that cos(x+z)-4ab{cos(x-y)}=1-2a×a-2b×b

If sin(x+y)=a and sin(x+z)=b , then prove that cos(x+z)-4ab{cos(x-y)}=

1.	If sin(x+y)=a and sin(x+z)=b , then prove that cos(x+z)-4ab{cos(x-y)}=1-2a×a-2b×b
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