Question

The equation of a parabola is $ {{x}^{2}}=-10y, $ then coordinates of focus are

• A. $ \left( 0,-\frac{5}{2} \right) $
• B. $ \left( 0,\frac{5}{2} \right) $
• C. $ \left( \frac{5}{2},0 \right) $
• D. $ \left( -\frac{5}{2},0 \right) $

Answer 1

Answer: (A)

Equation of parabola is
$ {{x}^{2}}=-10y $
On comparing with
$ {{x}^{2}}=-4ay $ we get $ -4a=-10 $ or $ a=\frac{10}{4}=\frac{5}{2} $
Hence, coordinates of focus $ =(0,-5/2) $