If 2.cos x + sin x = 1, then 7.cos x + 6.sin x =
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write the equation as
=> 2 * cos x = 1 - sin x
square both sides and use the identity cos ^ x + sin ^ x=1
you will get a quadratic in sin x which is of the form
=> 5 * sin ^ x - 2 * sin x - 3 = 0
solving this, we obtain the value of sin ^ x = 1 ; -3/5
find cos x and put the value in the given equation.