Question:medium

Find the slope of the normal to the curve \( y = 2x^2 + 3\sin x \) at the coordinate point where \( x = 0 \).

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Always read the question carefully to see if it asks for the slope of the tangent or the normal. Tangent is just the direct derivative value, while normal requires taking the negative reciprocal (\( -1/m \)). Skipping this inversion step is a very common cause of lost marks.
Updated On: Jun 3, 2026
  • \( -\frac{1}{3} \)
  • \( 3 \)
  • \( -3 \)
  • \( \frac{1}{3} \)
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The Correct Option is A

Solution and Explanation

Step 1: Understanding the Concept:
Calculus allows us to determine the geometric properties of a curve at any specific point using derivatives.
The first derivative of a function, denoted as \( \frac{dy}{dx} \) or \( f'(x) \), represents the slope of the tangent line touching the curve at that point.
A "Tangent" is a line that just grazes the curve at a point, reflecting the curve's direction at that instant.
A "Normal" line, on the other hand, is defined as the line that is perpendicular to the tangent at the point of tangency.
In coordinate geometry, the slopes of two perpendicular lines (\( m_1 \) and \( m_2 \)) have a specific relationship: their product is always \( -1 \).
This means that if we know the slope of the tangent, the slope of the normal is its negative reciprocal.
Step 2: Key Formula or Approach:
1. Find the general derivative \( \frac{dy}{dx} \) of the given curve.
2. Evaluate this derivative at the point \( x = 0 \) to find the tangent slope, \( m_t \).
3. Calculate the normal slope using the formula:
\[ m_n = -\frac{1}{m_t} \]
Step 3: Detailed Explanation:
The given equation of the curve is \( y = 2x^2 + 3\sin x \).
We apply the sum rule and power rule of differentiation. The derivative of \( x^2 \) is \( 2x \), and the derivative of \( \sin x \) is \( \cos x \).
\[ \frac{dy}{dx} = \frac{d}{dx}(2x^2) + \frac{d}{dx}(3\sin x) \]
\[ \frac{dy}{dx} = 4x + 3\cos x \]
We need to find the slope of the tangent at the specific point where \( x = 0 \).
Substituting \( x = 0 \) into the derivative expression:
\[ m_t = 4(0) + 3\cos(0) \]
Recalling trigonometric values, we know that \( \cos(0) = 1 \).
\[ m_t = 0 + 3(1) = 3 \]
So, the slope of the tangent line at the origin (or where \( x = 0 \)) is 3.
Since the question asks for the slope of the normal, we must take the negative reciprocal of the tangent's slope.
\[ m_{\text{normal}} = -\frac{1}{m_{\text{tangent}}} \]
\[ m_{\text{normal}} = -\frac{1}{3} \]
This value represents the steepness of the line perpendicular to the curve at \( x = 0 \).
Step 4: Final Answer:
The slope of the normal line at the given point is \( -\frac{1}{3} \).
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