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Questions  

If p1, p2 denote the lengths of the perpendiculars from the origin on the lines xseca+ycoseca=2a and x cos a + y sin a = a cos 2a respectively, 

a
4sin24α
b
4cos24α
c
4 cosec24α
d
4 sec24α

detailed solution

Correct option is C

p12+p22=4a2sec2⁡α+cosec2⁡α+a2cos2⁡2αcos2⁡α+sin2⁡α        =a2sin2⁡2α+cos2⁡2α=a2and   p12p22=a4sin2⁡2αcos2⁡2α=(1/4)a4sin2⁡4α∴p1p2+p2p12=p12+p222p12p22=4sin2⁡4α=4cosec2⁡4α.

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