Question

what will be cos(A-B)=?
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Answer 1

Just remember these two basics:

sin(A+B)= sinAcosB+cosAsinB (Remember)

Then, you can easily find sin(A-B).

sin(A-B)= sin(A+(-B))= sinAcos(-B)+cosAsin(-B)=sinAcosB+cosA(-sinB) {since;

cos(-X)=cosX

sin(-X)=sin(X)}

sin(A-B)=sinAcosB-cosAsinB

cos(A+B)=cosAcosB-sinAsinB (Remember)

cos(A-B)=cos(A+(-B))=cosAcos(-B)-sinAsin(-B)=cosAcosB-sinA(-sinB)

cos(A-B)=cosAcosB+sinAsinB

Answer 2

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