1.

Passage: For the parabola y2 = 4ax, the vertex is (0, 0), the focus is (a, 0) and the directrix is x + a = 0. Answer the following three questions.(i) The vertex of the parabola (y - 1)2 = 2(x - 1) is (A)  (1,0)(B)  (2,0) (C)  (1,1)(D)  (0,1)(ii)  Focus of the parabola y2 = 4(x - 1) is(A)  (1, 0)(B)  (2, 0)(C)  (1, 1)(D)  (2, 2)(iii)  The directrix of the parabola (y - 2)2 = 4(x - 1)(A)   x = 1(B)   x = -1(C)   x = 2 (D)  x =  0

Answer»

Correct option  (i)(c)(ii)(b)(iii)(d)

Explanation :

(i) The parabola is

Y2 = 4(1/2)(x)

where X = x - 1 and Y = y - 1. Therefore, the vertex is

(X = 0, Y = 0) = (x - 1 = 0, y -  1 =  0) = (1, 1)

 (ii)  y2 = 4(x -1) is Y2 = 4X where X = x - 1 and Y = y and a - 1. The focus is

(X = 1, Y = 0) =(x - 1 = 1,y = 0) = (2,0)

 (iii)  (y - 2)2 = 4(x - 1)  ⇒ Y2 = 4X where X = x - 1 and Y = y − 2. The directrix equation is

X = -a = -1

⇒ x - 1 = -1

⇒ x = 0



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