Q77 / 150 · MHT CET 2020 (16 Oct Shift 2) · Mathematics

The length of latus -rectum of the parabola $x^{2}+2 y=8 x-7$ is

A
8
Correct answer
B
2
C
6
D
4

Solution

We have, $\begin{array}{l} x^{2}+2 y=8 x-7 \\ x^{2}-8 x=-2 y-7 \\ x^{2}-8 x+16=-2 y-7+16 \\ (x-4)^{2}=-2 y+9 \\ (x-4)^{2}=-2(y-9 / 2) \end{array}$ $\therefore$ Length of latus rectum $=2$

Hence, the correct answer is option: 'B'.

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