Question

The reflection of the curve xy = 1 in the line y = 2x is the curve 12x² + rxy + sy² + t = 0, then the value of r is-

• A. –7
• B. 25
• C. –175
• D. None of these

Answer 1

Answer: (A)

–7

Answer 2

The reflection of (a, b) in the line y = 2x is

(a₁, b₁) º $\left( \frac { 4 \beta - 3 \alpha } { 5 } , \frac { 4 \alpha + 3 \beta } { 5 } \right)$

Since a₁b₁ = 1 ̃ $\left( \frac { 4 \alpha + 3 \beta } { 5 } \right)$ = 1

̃ 12a² –7 ab –12b² + 25 = 0