Question Details

The points at which the tangents to the curve y = x² – 12x +18 are parallel to x-axis are

Options

A

(2, – 2), (- 2, -34)

B

(2, 34), (- 2, 0)

C

(0, 34), (-2, 0)

D

(2, 2),(-2, 34)

Correct Answer :

(2, 2),(-2, 34)

Solution :

The correct option is (2, 2), (-2, 34).

Let's understand why this is the correct answer step-by-step.

Step 1: Understand the condition for a tangent to be parallel to the x-axis
The slope of the tangent to a curve at any point is given by the derivative of the curve's equation, which is denoted as:
dy dx
Since the x-axis is a horizontal line, its slope is equal to 0. For a tangent line to be parallel to the x-axis, its slope must also be equal to 0. Thus, we set:
dy dx = 0

Step 2: Differentiate the given curve equation
Note: Based on the provided correct option, the curve equation is of the form y=x3−12x+18 (where the exponent of the first term is 3). Let us differentiate this function with respect to x:
dy dx = d dx x3 − 12 x + 18
Using standard differentiation rules (the power rule), we get:
dy dx = 3 x2 − 12

Step 3: Solve for the x-coordinates
Now, set the derivative equal to 0 to find the points where the tangent is horizontal:
3 x2 − 12 = 0
Dividing both sides by 3:
x2 − 4 = 0
x2 = 4
Taking the square root on both sides yields:
x = ± 2

Step 4: Find the corresponding y-coordinates
We substitute these x values back into the original curve equation y=x3−12x+18 to find their corresponding y-coordinates.

Case 1: When x=2
y = (2)3 − 12 (2) + 18
y = 8 − 24 + 18
y = 2
This gives us the point (2, 2).

Case 2: When x=−2
y = (−2)3 − 12 (−2) + 18
y = − 8 + 24 + 18
y = 34
This gives us the point (-2, 34).

Thus, the coordinates of the points where the tangents to the curve are parallel to the x-axis are (2, 2) and (-2, 34).

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