If x+cos q = sec q, y + cos8q=sec8qthen(x2+4y2+4)(dydx)2=
A
8
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B
16
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C
64
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D
49
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Solution
The correct option is C 64 dydx=dydqdxdq=8sec8qtanq+8cos7qsinqsecqtanq+sinq =8tanq(sec8q+cos8q)tanq(secq+cosq) (dydx)2=64(sec8q+cos8q)2(secq+cosq)2 =64[(sec8q−cos8q)2+4][(secq−cosq)2+4] =64(y2+4)x2+4 (x2+4y2+4)(dydx)2=64