The tangents to the parabola y = 4ax from an external point P mak

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 Multiple Choice QuestionsMultiple Choice Questions

441.

Let M be the foot of the perpendicular from a point P on the parabola y = 8(x - 3) onto its directrix and let S be the focus ofthe parabola. If  SPM is an equilateral triangle, then P is equal to

  • (43, 8)

  • (8, 43)

  • (9, 43)

  • (43, 9)


442.

Consider the circle x2 + y - 4x - 2y + c = 0 whose centre is A(2, 1). If the point P(10, 7) is such that the line segment PA meets the circle in Q with PQ = 5, then c is equal to

  • - 15

  • 20

  • 30

  • - 20


443.

The foci of the ellipse x216 + y2b2 = 1 and the hyperbola x2144 - y281 = 125 coincide. Then, the value of b2 is 

  • 5

  • 7

  • 9

  • 1


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444.

The tangents to the parabola y = 4ax from an external point P make angles θ1 and θ2, with the axis of the parabola. Such that tanθ1 + tanθ2 = b where b is constant. Then P lies on

  • y = x + b

  • y + x = b

  • y = xb

  • y = bx


D.

y = bx

d We have

P is intersecting point of tangents at A(at12, 2at1) and B(at22, 2at2)Pat1t2, at1 + t2Slopeof line PAie tanθ1 = 2at1 - at1 - at2at12 - at1t2= at1 - t2at1t1 - t2= 1t1Similarly, slope of line PB tanθ2 = 2at1 - at1 - at2at12 - at1t2 = at2 - t1at2t2 - t1 =  1t2It is given thattanθ1 + tanθ2 = b 1t1 + 1t2 = b t2 + t1 = bt1t2 ya = bxa      x = at1t2, y = at1 + t2 y = bx P lies on the line y = bx


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445.

The area (in sq. units) of the largest rectangle ABCD whose vertices A and B lie on the x-axis and vertices C and D lie on the parabola, y = x2 – 1 below the x-axis, is

  • 133

  • 43

  • 433

  • 233


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