JEE Main2013MathematicsCircleActual
Given : A circle, 2 x 2 + 2 y 2 = 5 and a parabola, y 2 = 4 5 x . Statement - I : An equation of a common tangent to these curves is y = x + 5 . Statement - II : If the line, y = m x + 5 m m ≠ 0 is their common tangent, then m satisfies m 4 - 3 m 2 + 2 = 0 .
Options
- AStatement - I is true; Statement - II is false.
- BStatement - I is false; Statement - II is true.
- CStatement - I is true; Statement - II is true; Statement - II is a correct explanation for statement - I .
- DStatement - I is true; Statement - II is true; Statement - II is not a correct explanation for statement - I .
Correct answer
D. Statement - I is true; Statement - II is true; Statement - II is not a correct explanation for statement - I .
Step-by-step solution
Tangent to y 2 = 4 5 x will be y = m x + 5 m As tangent to x 2 + y 2 = 5 2 will be y = m x ± 5 2 1 + m 2 Hence for common tangent 5 m = 5 2 1 + m 2 ⇒ m 4 + m 2 - 2 = 0 ⇒ m 2 = 1 , m 2 = − 2 (Not Possible) ⇒ m = ± 1 Hence common tangent is y = x + 5 Both the statements are correct The values of m also satisfy the equation in statement - II but it is not a correct explanation for statement - I .