The intercepts on x-axis made by tangents to the curve, , which are parallel to the line y = 2x, are equal to:
(1) (2)
(3)
(4)
[JEE Main 2013]
Solution
If x > 0,
Slope of tangent =
Since the tangent is parallel to the line y = 2x whose slope = 2,
So, the point of contact is (2, 2) and the equation of the tangent is,
y – 2 = 2(x – 2)
Or, y = 2x – 2 whose intercept on the x-axis is 1.
If x < 0,
Slope of tangent =
Since the tangent is parallel to the line y = 2x whose slope = 2,
or x = -2
So, the point of contact is (-2, -2) and the equation of the tangent is,
y + 2 = 2(x + 2)
Or, y = 2x + 2 whose intercept on the x-axis is -1. Hence, option (1).