Q20 of 292 Page 564

Find the point on the curve at which the tangent passes through the origin.

If tangent is pass through origin it means that equation of tangent is y = mx

Let us suppose that tangent is made at point (x1, y1)


y1 = x12 + 3x1 + 4 …(1)



m at (x1, y1) = 2x1 + 3


Equation of tangent : y1 = (2x1 + 3)x1 …(2)


On compairing eq(1) and eq(2)


x12 + 3x1 + 4 = (2x1 + 3)x1


x12 – 4 = 0 x1 = 2 and -2


At x1 = 2, y1 = 14


At x1 = -2, y1 = 2


So, required points are (2, 14) and (-2, 2)


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