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← JEE Main 2022 · 24 Jun · Shift 1
MathematicsSingle correct+4 / -1Question 15 of 90

JEE Main 2022 · 24 Jun · Shift 1, Mathematics question 15

Let λx−2y=μ\lambda x-2y=\mu be a tangent to the hyperbola a2x2−y2=b2a^2x^2-y^2=b^2. Then (λa)2−(μb)2\left(\dfrac\lambda a\right)^2-\left(\dfrac\mu b\right)^2 is equal to :

Choose one option
Answer and worked solution

Official answer: D

Standard form. The hyperbola is x2b2/a2−y2b2=1\dfrac{x^2}{b^2/a^2}-\dfrac{y^2}{b^2}=1 and the line is y=λ2x−μ2y=\dfrac\lambda2x-\dfrac\mu2.

Tangency (c2=A2m2−B2c^2=A^2m^2-B^2): μ24=b2a2⋅λ24−b2\dfrac{\mu^2}4=\dfrac{b^2}{a^2}\cdot\dfrac{\lambda^2}4-b^2.

Rearrange. Dividing by b2/4b^2/4: (λa)2−(μb)2=4\left(\dfrac\lambda a\right)^2-\left(\dfrac\mu b\right)^2=4.

(D)