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Given 
f(x)=2x-3, find 
f^(')(-2) using the definition of a derivative.

Given f(x)=2x3 f(x)=2 x-3 , find f(2) f^{\prime}(-2) using the definition of a derivative.

Full solution

Q. Given f(x)=2x3 f(x)=2 x-3 , find f(2) f^{\prime}(-2) using the definition of a derivative.
  1. Define derivative limit: To find f(2)f'(-2), we need to use the definition of the derivative, which is the limit of the average rate of change as the change in xx approaches 00.
  2. Substitute values: The definition of the derivative is f(x)=limh0f(x+h)f(x)hf'(x) = \lim_{h \to 0} \frac{f(x+h) - f(x)}{h}.
  3. Calculate f(2+h)f(-2+h): Substitute xx with 2-2 and f(x)f(x) with 2x32x-3 into the definition: f(2)=limh0f(2+h)f(2)hf^{\prime}(-2) = \lim_{h\to 0} \frac{f(-2+h) - f(-2)}{h}.
  4. Calculate f(2)f(-2): Calculate f(2+h)f(-2+h): f(2+h)=2(2+h)3=4+2h3f(-2+h) = 2(-2+h)-3 = -4+2h-3.
  5. Substitute into limit: Calculate f(2)f(-2): f(2)=2(2)3=43=7f(-2) = 2(-2)-3 = -4-3 = -7.
  6. Simplify expression: Substitute f(2+h)f(-2+h) and f(2)f(-2) into the limit: f(2)=limh0(4+2h3)(7)hf^{\prime}(-2) = \lim_{h\to 0} \frac{(-4+2h-3) - (-7)}{h}.
  7. Further simplify: Simplify the expression inside the limit: f(2)=limh0[2h4+3+7]hf^{\prime}(-2) = \lim_{h \to 0} \frac{[2h-4+3+7]}{h}.
  8. Divide by h: Further simplify the expression: f(2)=limh02h+6hf'(-2) = \lim_{h\to 0} \frac{2h+6}{h}.
  9. Identify mistake: Divide each term by hh: f(2)=limh0[2+6h]f'(-2) = \lim_{h \to 0} [2 + \frac{6}{h}].
  10. Identify mistake: Divide each term by hh: f($2f'(\$-2) = \lim_{h\to00} [22 + \frac{66}{h}]\).As hh approaches 00, the term 6h\frac{6}{h} approaches infinity, which is incorrect since we expect a finite number for the derivative. There's a mistake in the previous step.

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