cos(A-B)=cosAcosB + sinAsinB

[Guest]

Prove that:
cos(A-B)=cosAcosB + sinAsinB by using vector properties

[adamsmith]

Prove that: cos(A-B)=cos A cos B + sin A sin B by using vector properties
let p and q are two vector
|p|=|q|=1
just write out the scalar product of p bar and q bar twice
we can write scalar product of p and q like below
p bar. Q bar=|p||q| cos (A-B)
=1.1.cos(A-B)
=Cos (A-B)
and p bar .q bar =cos A cos B +sin A sin B
there for cos(A-B)=cos A cos B +sin A sin B

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