Question

Find the length of sub -tangent of parabola $y^2=12x$ at $(3,6)$.

• A. 6
• B. 8
• C. 10
• D. None of the above

Answer 1

The correct option is A 6

$y^2=12x$

$\therefore \frac{dx}{dy}=\frac{y}{6}$

Length of subtangent $=\left|y\right(\frac{dx}{dy}\left)\right|$

$=\left|\frac{y^2}{6}\right|$

So, the length of subtangent at $(3,6)=\left|\frac{6^2}{6}\right|=6$ units

So, the answer is option (A).