SOLUTION: How can i verify that cos(A+B)= 1- Tan(A)Tan(B)/sec(A)sec(B)

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Question 531423: How can i verify that cos(A+B)= 1- Tan(A)Tan(B)/sec(A)sec(B)
Answer by lwsshak3(11628) About Me  (Show Source):
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How can i verify that cos(A+B)= 1- Tan(A)Tan(B)/sec(A)sec(B)
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starting with right side
1- Tan(A)Tan(B)/sec(A)sec(B)
[1-sinA/cosA*sinB/cosB]/(1/cosA)(1/cosB)
[(cosAcosB-sinAsinB)/cosAcosB]/(1/cosAcosB)
(cosAcosB-sinAsinB)
Identity: Cos(s+t)=cos s cost-sins sin t
(cosAcosB-sinAsinB)=Cos(A+B)
verified: (right side=left side