Definite integral of the rate of change of a quantity over an interval interpreted as the change of the quantity over the interval - AP Calculus AB

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Question

If g(x)=\int_{0}^{x^2}f(t)dt, then which of the following is equal to g'(x)?

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Answer

According to the Fundamental Theorem of Calculus, if we take the derivative of the integral of a function, the result is the original function. This is because differentiation and integration are inverse operations.

For example, if h(x)=\int_{a}^{x}f(u)du, where is a constant, then h'(x)=f(x).

We will apply the same principle to this problem. Because the integral is evaluated from 0 to x^{2}, we must apply the chain rule.

g'(x)=\frac{d}{dx}\int_{0}^{x^{2}}f(t)dt=f(x^{2})\cdot \frac{d}{dx}(x^{2})

=2xf(x^{2})

The answer is 2xf(x^{2}).

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