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Question


If  x=a sec θ+b tan θ and y=a tan θ+b sec θ, then x2y2a2b2= ___


Options:
A .   2
B .   1
C .   0
D .   - 1
Answer: Option B
:
B

x=a sec θ+b tan θ, y=a tan θ+b sec θ
Squaring both sides we get,
x2=(a sec θ+b tan θ)2, y2=(a tan θ+b sec θ)2
x2=a2 sec2 θ+2ab sec θ tan θ+b2 tan2 θy2=a2 tan2 θ+2ab sec θ tan θ+b2 sec2 θ                                                           –––––––––––––––––––––––––––––––––––––––––––Subtracting, x2y2=a2(sec2 θtan2 θ)+b2(tan2 θsec2 θ)
x2y2=a2(sec2 θtan2 θ)b2(sec2 θtan2 θ)
x2y2=a2b2(sec2 θtan2 θ=1)
x2y2a2b2=1



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