• # question_answer If one end of a focal chord of the parabola, ${{y}^{2}}=16x$ is at (1, 4), then the length of this focal chord is [JEE Main 9-4-2019 Morning] A) 25       B) 24C) 20                               D) 22

${{y}^{2}}=4ax=16x\Rightarrow a=4$ $A(1,4)\Rightarrow 2.4{{t}_{1}}=4\Rightarrow {{t}_{1}}=\frac{1}{2}$ $\therefore$ length of focal chord$=a{{\left( t+\frac{1}{t} \right)}^{2}}$ $=4{{\left( \frac{1}{2}+2 \right)}^{2}}=4.\frac{25}{4}=25$