Mathematics Grade 12 15 min

Find values of derivatives using limits

Find values of derivatives using limits

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1

Introduction & Learning Objectives

Learning Objectives Define the derivative as the limit of the difference quotient. Calculate the derivative of a function at a specific point using the limit definition. Find the general derivative function, f'(x), for polynomial functions using the limit definition. Find the derivative function, f'(x), for simple radical and rational functions using the limit definition. Connect the value of the derivative at a point to the slope of the tangent line at that point. Use the alternative form of the derivative definition to find the derivative at a specific point. Ever wonder how a police officer's radar gun calculates your car's exact speed at one instant, not just your average speed over a trip? 🚓 That's the power of instantaneous rates of change! I...
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Key Concepts & Vocabulary

TermDefinitionExample Secant LineA line that passes through two distinct points on a curve. The slope of the secant line represents the average rate of change of the function between those two points.For the curve y = x², the line passing through the points (1, 1) and (3, 9) is a secant line. Its slope is (9-1)/(3-1) = 4. Tangent LineA line that touches a curve at a single point and has the same direction as the curve at that point. The slope of the tangent line represents the instantaneous rate of change of the function at that point.For the curve y = x², the tangent line at the point (1, 1) has a slope of 2. Difference QuotientThe expression (f(x + h) - f(x)) / h. It represents the slope of the secant line between the points (x, f(x)) and (x + h, f(x + h)).For f(x) = x², the difference...
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Core Formulas

The Limit Definition of the Derivative f'(x) = \lim_{h \to 0} \frac{f(x + h) - f(x)}{h} This is the primary formula used to find the derivative as a function, f'(x). It calculates the instantaneous rate of change for any 'x' by finding the limit of the slope of the secant line as the distance between the points, 'h', shrinks to zero. The Alternative Form of the Derivative at a Point f'(a) = \lim_{x \to a} \frac{f(x) - f(a)}{x - a} This is an alternative formula used to find the derivative at a single, specific point, x = a. It is conceptually the same as the primary definition but can sometimes be algebraically simpler for certain functions.

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Sample Practice Questions

Challenging
Find the derivative function, f'(x), for the rational function f(x) = \frac{x+1}{x} using the limit definition.
A.\frac{-1}{x^2}
B.\frac{1}{x^2}
C.1
D.\frac{2}{x^2}
Challenging
Use the alternative form of the derivative to find f'(a) for the function f(x) = \sqrt{x}.
A.2\sqrt{a}
B.\frac{1}{2\sqrt{a}}
C.\frac{1}{\sqrt{a}}
D.\frac{a}{2}
Challenging
First, find the derivative of f(x) = x³ - 12x using the limit definition. Then, find the positive value of x for which the tangent line to f(x) is horizontal.
A.4
B.3
C.2
D.1

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