Question

If b and c are the length of the segments of and focal chord of a parabola y² = 4ax. Then the length of the semi-latus rectum is –

• A. $\frac{b + c}{2}$
• B. $\frac{bc}{b + c}$
• C. $\frac{2bc}{b + c}$
• D. $\sqrt{bc}$

Answer 1

Answer: (C)

$\frac{2bc}{b + c}$

Answer 2

From theory, L.R.=4l₁l₂/l₁+l₂

\L.R./2=2l₁l₂­**/**l₁+l₂

i.e. semi-latus rectum = 2bc/(b+c)