Question
If x=a sec θ+b tan θ and y=a tan θ+b sec θ, then x2−y2a2−b2= ___
Answer: Option B
:
B
x=asecθ+btanθ,y=atanθ+bsecθ
Squaring both sides we get,
x2=(asecθ+btanθ)2,y2=(atanθ+bsecθ)2
∴x2=a2sec2θ+2absecθtanθ+b2tan2θy2=a2tan2θ+2absecθtanθ+b2sec2θ−−−–––––––––––––––––––––––––––––––––––––––––––––Subtracting,x2−y2=a2(sec2θ−tan2θ)+b2(tan2θ−sec2θ)
x2−y2=a2(sec2θ−tan2θ)−b2(sec2θ−tan2θ)
x2−y2=a2−b2……(sec2θ−tan2θ=1)
∴x2−y2a2−b2=1
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:
B
x=asecθ+btanθ,y=atanθ+bsecθ
Squaring both sides we get,
x2=(asecθ+btanθ)2,y2=(atanθ+bsecθ)2
∴x2=a2sec2θ+2absecθtanθ+b2tan2θy2=a2tan2θ+2absecθtanθ+b2sec2θ−−−–––––––––––––––––––––––––––––––––––––––––––––Subtracting,x2−y2=a2(sec2θ−tan2θ)+b2(tan2θ−sec2θ)
x2−y2=a2(sec2θ−tan2θ)−b2(sec2θ−tan2θ)
x2−y2=a2−b2……(sec2θ−tan2θ=1)
∴x2−y2a2−b2=1
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