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Question
Prove the following:
`sqrt(2)cos (pi/4 - "A")` = cos A + sin A
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Solution
L.H.S. = `sqrt(2)cos(pi/4 - "A")`
= `sqrt(2)(cos pi/4 cos"A" + sin pi/4 sin"A")`
= `sqrt(2)(1/sqrt(2) xx cos"A" + 1/sqrt(2) xx sin"A")`
= `sqrt(2)/sqrt(2)(cos"A" + sin"A")`
= cos A + sin A
= R.H.S.
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