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The points at which the tangents to the curve y = x3 – 12x + 18 are parallel to x-axis are ______. - Mathematics

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Question

The points at which the tangents to the curve y = x3 – 12x + 18 are parallel to x-axis are ______.

Options

  • (2, –2), (–2, –34)

  • (2, 34), (–2, 0)

  • (0, 34), (–2, 0)

  • (2, 2), (–2, 34)

MCQ
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Solution

The points at which the tangents to the curve y = x3 – 12x + 18 are parallel to x-axis are (2, 2), (–2, 34).

Explanation:

Given that y = x3 – 12x + 18

Differentiating both sides w.r.t. x, we have

⇒ `"dy"/"dx"` = 3x2 – 12

Since the tangents are parallel to x-axis, then `"dy"/"dx"` = 0

∴ 3x2 – 12 = 0

⇒ x = ± 2

∴ `y_(x = 2)` = (2)3 – 12(2) + 18

= 8 – 24 + 18

= 2

`y_(x = -2)` = (– 2)3 – 12 (– 2) + 18

= – 8 + 24 + 18

= 34

∴ Points are (2, 2) and (– 2, 34).

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Chapter 6: Application Of Derivatives - Exercise [Page 139]

APPEARS IN

NCERT Exemplar Mathematics [English] Class 12
Chapter 6 Application Of Derivatives
Exercise | Q 42 | Page 139

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