If $\theta = 3\, \alpha$ and $sin\, \theta =$ $\frac{a}{{\sqrt {{a^2}\,\, + \,\,{b^2}} }}$. The value of the expression , $a \,cosec\, \alpha - b \,sec\, \alpha$ is
If $\theta = 3\, \alpha$ and $sin\, \theta =$ $\frac{a}{{\sqrt {{a^2}\,\, + \,\,{b^2}} }}$. The value of the expression , $a \,cosec\, \alpha - b \,sec\, \alpha$ is
- A
$\frac{1}{{\sqrt {{a^2}\,\, + \,\,{b^2}} }}$
- B
$2 \sqrt {{a^2}\,\, + \,\,{b^2}}$
- C
$a + b$
- D
none
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