Engineering
Mathematics
Tangent and Normal
Question

Let a, b, c are such that the curve y = ax2 + bx + c is tangent to y = 3x – 3 at (1, 0) and is also tangent to y = x + 1 at (3, 4). Then

2a – b – 4c = 9

ab = 2

2a + b = 3

a + c = – 4

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Solution

dydx]x=1 = 2ax + b = 2a + b = 3        ….…(1)
and dydx]x=3 = 6a + b = 1                 ….…(2)
(1) & (2)
⇒ a = 12 ; b = 4 and c = 72.