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how to prove cos(pi/4 – theta)cos(pi/4- fi) -sin(pi/4 – theta)sin(pi/4 +fi) = sin(theta + fi)

how to prove cos(pi/4 – theta)cos(pi/4- fi) -sin(pi/4 – theta)sin(pi/4 +fi) = sin(theta + fi)
 

Grade:11

1 Answers

Harsh Jain
31 Points
5 years ago
Firstly multiply and divide by 2 in LHs.1/2[{2cos(pi/4-theta)cos{(pi/4-fi)}-{2sin(pi/4-theta)sin(pi/4-fi}]Then apply identity of 2casAcosB and 2 sin AsinB in the equationFinally u will get 1/2{2[cos(pi/2-theta-fi)]}Which gives u sin{theta +fi}

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