The points at which the tangents to the curve y = x3 – 12x + 18 are parallel to x-axis are:
Given the equation of the curve is
y = x3 – 12x + 18
Differentiating on both sides with respect to x, we get
Applying the sum rule of differentiation, we get
We know derivative of a constant is 0, so above equation becomes
Applying the power rule we get
So, the slope of line parallel to the x-axis is given by
So equating equation (i) to 0, we get
3x2-12=0
⇒ 3x2=12
⇒ x2=4
⇒ x=±2
When x=2, the given equation of curve becomes,
y = x3 – 12x + 18
⇒ y = (2)3 – 12(2) + 18
⇒ y = 8– 24 + 18
⇒ y = 2
When x=-2, the given equation of curve becomes,
y = x3 – 12x + 18
⇒ y = (-2)3 – 12(-2) + 18
⇒ y = -8+24 + 18
⇒ y = 34
Hence the points at which the tangents to the curve y = x3 – 12x + 18 are parallel to x-axis are (2, 2) and (-2, 34).
So the correct option is option D.