Question

The equation of the common tangent to curve y² = 8x and

xy = –1 is

• A. 3y = 9x + 2
• B. y = 2x + 1
• C. 2y = x + 8
• D. y = x + 2

Answer 1

Answer: (B)

y = 2x + 1

Answer 2

Any tangent to y² = 8x is

y = mx + $\frac{2}{m}$ .... (i)

this will also be –tangent to xy = –1 ....(ii)

Solve (i) and (ii) to get quadrate in X, Now

D = 0