if (sin alpha)/a=(cos alpha)/b.then asin 2alpha+bcos 2alpha=?

b is the answer..
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QUESTION:sin alpha/a =cos alpha /b then a (sin 2 alpha)(alpha+b(cos2 alpha) = ANSWER: cos alpha /a=sin alpha/b then a cos2 alpha + b sin2 alpha=a If sin alpha=3/5 where π/2
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multiply by 2sin[A] on both sides of cos[A]/a=sin[A]/b
you will have smthng roughly like this:
2sin[A] x cos[A]/a=2sin[A] x sin[A]/b
since,2sin[A].cos[A] is the formula of sin2[A],lets put sin2[A]
cross multiply:

from the formula cos2B=1-2sin^2B we can get 2sin^2B=1-cos2B lets put this on the RHS

open the bracket:

you can prove the same for 'b' by multiplying and dividing by 2cos[A]

hope it is helpful
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