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    If tan θ=batan\spaceθ=\tfrac{b}{a}tan θ=ab​​, then a cos θ + b sin θa cos θ − b 
    Question

    If tan θ=batan\spaceθ=\tfrac{b}{a}​, then a cos θ + b sin θa cos θ  b sin θ\tfrac{a\space cos \space θ\space+\space b\space sin\space θ}{{a\space cos \space θ\space-\space b\space sin\space θ}}​ = __________

    A.

    a2b2a2+b2\tfrac{a^2-b^2}{a^2+b^2}​​

    B.

    aba+b\tfrac{a-b}{a+b}​​

    C.

    a2+b2a2b2\tfrac{a^2+b^2}{a^2-b^2}​​

    D.

    a+bab\tfrac{a+b}{a-b}​​

    Correct option is C

    Given:
    tan θ=batan\spaceθ=\frac{b}{a}​​, then a cos θ + b sin θa cos θ  b sin θ\tfrac{a\space cos \space θ\space+\space b\space sin\space θ}{{a\space cos \space θ\space-\space b\space sin\space θ}}​​ = _________

    Solution:

    a cos θ + b sin θa cos θ  b sin θ\frac{a\space cos \space θ\space+\space b\space sin\space θ}{{a\space cos \space θ\space-\space b\space sin\space θ}}

    Divided by cos θ ,we have
    a  + b tan θa   b tan θ\frac{a\space \space+\space b\space tan\space θ}{{a\space\space-\space b\space tan\space θ}}

    =a  +b2aa  b2a\frac{a\space \space+\frac{b^2}{a}}{{a\space\space-\frac{b^2}{a}}}

    =a2+b2a2b2\frac{a^2+b^2}{a^2-b^2}

    Option (C) is right.

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