Engineering
Mathematics
Tangent and Normal
Question

The normal to the curve y (x – 2) (x – 3) = x + 6 at the point where the curve intersects the y‑axis passes through the point

(12, 12)

(−12, −12)

(12, −13)

(12, 13)

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Solution

Given curve y × (x – 2) (x – 3) = (x + 6)                           …….(1)

Let required point is P, where curve intersects y‑axis.

For P, put x = 0 ⇒ y = 1, so P(0, 1)

Equation (1) differentiate w.r.t. x

(x – 2) (x – 3) dydx + y (2x – 5) = 1

⇒(dydx)(0, 1) =1

Slope of normal = – 1

Equation of normal at P (0, 1) ⇒ (y – y1) = m (x – x1)

y – 1 = – 1 (x – 0) ⇒ x + y = 1                            …….(2)

By option (12, 12) will satisfy x + y = 1.