If the line $y$ $\cos \alpha = x\sin \alpha + a\cos \alpha $ be a tangent to the circle ${x^2} + {y^2} = {a^2}$, then
If the line $y$ $\cos \alpha = x\sin \alpha + a\cos \alpha $ be a tangent to the circle ${x^2} + {y^2} = {a^2}$, then
- A
${\sin ^2}\alpha = 1$
- B
${\cos ^2}\alpha = 1$
- C
${\sin ^2}\alpha = {a^2}$
- D
${\cos ^2}\alpha = {a^2}$
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- [KVPY 2013]
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