1.

The value of `thetain(-pi/2, pi/2)` for which the line `y=x" cos "theta+4" cos" ^(3)" "theta-14" cos "theta-1` is a normal to the parabola `y^(2)=16x,` isA. `pi//3`B. `pi//6`C. `pi//9`D. `pi//4`

Answer» Correct Answer - C
The slope of the given line is m = cos `theta`.
We know that the line y = mx + c is a normal to the parabola `y^(2)=4ax`, if `c=-2am-am^(3)`. Therefore, the given line will be a normal to the parabola `y^(2)=16x,` is
`4 cos^(3)theta-14costheta-1=-8costheta-4cos^(2)theta`
`rArr" "8cos^(3)theta-6costheta=1`
`rArr" "2(4cos^(3)theta-3costheta)=1`
`rArr" "2cos3theta=1rArrcos3theta=1/2rArr3theta=pi/3theta=pi/9`


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