Q. Using the definition of the derivative, find f′(x). f(x)=−x2+6x−7
Definition of Derivative: The definition of the derivative f′(x) is the limit as h approaches 0 of the difference quotient hf(x+h)−f(x). Let's apply this definition to the function f(x)=−x2+6x−7.
Calculate f(x+h): First, we need to calculate f(x+h). This means we substitute x+h into the function in place of x:f(x+h)=−(x+h)2+6(x+h)−7.
Form Difference Quotient: Next, we form the difference quotient [f(x+h)−f(x)]/h:h[f(x+h)−f(x)]=h[−x2−2xh−h2+6x+6h−7]−[−x2+6x−7].
Simplify Difference Quotient: We simplify the difference quotient by canceling out the terms that appear in both f(x+h) and f(x):hf(x+h)−f(x)=h−x2−2xh−h2+6x+6h−7+x2−6x+7\= \frac{−2xh - h^2 + 6h}{h}.
Factor Out h: Now, we can factor out h from the numerator: hf(x+h)−f(x)=hh(−2x−h+6).
Take Limit: We cancel h from the numerator and denominator: hf(x+h)−f(x)=−2x−h+6.
Take Limit: We cancel h from the numerator and denominator: hf(x+h)−f(x)=−2x−h+6. Finally, we take the limit as h approaches 0: f′(x)=limh→0[−2x−h+6] = −2x+6.
More problems from Find derivatives of using multiple formulae