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CBSE Class 12 Maths 2010 Solved Paper
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Question : 20 of 29
Marks:
+1,
-0
Find the equations of the normals to the curve y = x3 + 2x + 6 which are parallel to the line x + 14y + 4 = 0.
Solution:
Equation of the curve is y = + 2x + 6 Slope of the normal at point (x, y) = = + 2 On substitution, we get Slope of the normal = ... (1) Normal to the curve is parallel to the line x + 14y + 4 = 0, i.e. y = - So the slope of the line is the slope of the normal. Slope of the line is - = ⇒ + 2 = 14 ⇒ = 12 ⇒ = 4 ⇒ x = ± 2 When x = 2, y = 18 and when x = - 2, y = - 6 Therefore, there are two normals to the curve y = + 2x + 6. Equation of normal through point (2, 18) is given by: y - 18 = (x - 2) ⇒ 14y - 252 = - x + 2 ⇒ x + 14y - 254 = 0 Equation of normal through point (-2,-6) is given by: y - (- 6) = (x - (- 2)) ⇒ 14y + 84 = - x - 2 ⇒ x + 14y + 86 = 0 Therefore, the equation of normals to the curve are x + 14y – 254 = 0 and x + 14y + 86 = 0
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