1.

If the tangent to the ellipse x2 + 4y2 = 16 at the point P (θ) is a normal to the circle x2 + y2 – 8x – 4y = 0 then θ equals(a)  π/2(b)  π/4(c)  0(d)  -π/4 

Answer»

Correct option  (a) , (c)

Explanation:

Given ellipse is  x2/16 + y2/4 = 1

Equation of tangent at P (θ) is P(acosθ ,bsinθ) i.e. P (4cosθ , 2sinθ) is

4x cosθ/16 + 2ysin θ/4 ....(1)

xcosθ  + 2ysinθ = 4  .......(1)

(1) is a normal to the circle x+ y– 8x – 4y = 

The equation (1) passes through the centre (4,2) of the circle. 

4cosθ + 4sinθ = 4

cosθ  + sinθ = 1

squaring

1 + sin2 = 1

sin2θ = 0

2θ = 0 or π

Hence, θ = 0 or π



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