1980

JEE Main 1980 Mathematics question on Straight Lines and Pair of Lines

The point (4, 1) undergoes the following three transformations successively
I. Reflection about the line y=xy = x.
II. Transformation through a distance 2 units along the positive direction of X-axis.
III. Rotation through an angle π4\frac{\pi}{4} about the origin in the counter clockwise direction.
Then, the final position of the point is given by the coordinates
  1. A.
    (12,72)\left(\dfrac{1}{\sqrt{2}}, \dfrac{7}{\sqrt{2}}\right)
  2. B.
    (−2,72)(-\sqrt{2}, 7\sqrt{2})
  3. C.
    (−12,72)\left(-\dfrac{1}{\sqrt{2}}, \dfrac{7}{\sqrt{2}}\right)
  4. D.
    (2,72)(\sqrt{2}, 7\sqrt{2})
Show answer and solution

Correct option: C

Solution

After reflection about y = x: (4,1) → (1,4).

After translation 2 units along positive x-axis: (1,4) → (3,4).

After rotation by π/4 counterclockwise: new coordinates are (x cosθ - y sinθ, x sinθ + y cosθ) = (3·(1/√2) - 4·(1/√2), 3·(1/√2) + 4·(1/√2)) = (-1/√2, 7/√2).

[1980]

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