Question

Difficulty: EasyTangents and Normals to Curves

What is the gradient of the normal line to the curve y=x23x+5y = x^2 - 3x + 5 at the point where x=1x = 1?

Answer: 1

Answer

The gradient of the normal line to the curve at x=1x = 1 is 1.
Differentiating y=x23x+5y = x^2 - 3x + 5 gives dydx=2x3\frac{dy}{dx} = 2x - 3. Evaluating this derivative at x=1x = 1 gives the tangent gradient mt=1m_t = -1. Because the normal line is perpendicular to the tangent, its gradient is mn=1mt=11=1m_n = -\frac{1}{m_t} = -\frac{1}{-1} = 1.

Step-by-Step Solution

1
Differentiate the function with respect to x
dydx=2x3\frac{dy}{dx} = 2x - 3
The derivative of a function gives the slope of the tangent line at any given x-coordinate.
2
Evaluate the derivative at x = 1
m_t = -1
Substituting the given point's x-coordinate into the gradient function yields the slope of the tangent.
3
Calculate the negative reciprocal of the tangent slope
m_n = 1
Since the normal line is perpendicular to the tangent line, its gradient is m_n = -1 / m_t.

Key Concept

Gradient of a Normal Line
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