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Questions  

 If xcosα+ysinα=4 is tangent to x225+y29=1 , then  the value of α is 

a
tan−1⁡(3/7)
b
tan−1⁡(7/3)
c
tan−1⁡(3/7)
d
tan−1⁡(3/7)

detailed solution

Correct option is A

xcos⁡α+ysin⁡α=4∴ y=(−cot⁡α)x+4cosec⁡α∴ m=−cot⁡α,c=4cosec⁡α,a2=25,b2=9 Now c2=a2m2+b2∴    16cosec2⁡α=25cot2⁡α+9∴    161+cot2⁡α=25cot2⁡α+9∴     7=9cot2⁡α⇒cot⁡α=73⇒tan⁡α=37∴    α=tan−1⁡(3/7)

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