# Math Help - Solving Integral

1. ## Solving Integral

I don't understand integration and differentiation very well, could someone please explain how this is true;

Thanks.

2. Note that $\frac{d}{dx} \ln x = \frac{1}{x}$.

The Fundamental Theorem of Calculus states that if F'(x) is the derivative of F(x), then $\int _a ^b F'(x) \cdot dx = F(b) - F(a)$.

In your question, this means $\int _{0.025} ^{0.075} \frac{1}{r} \cdot dr = \ln (0.075) - \ln (0.025)$, which is $\ln \left(\frac{0.075}{0.025}\right)$ by the rules of logarithms.

3. That's great, thanks for your help!

I need to learn the rules of calculus!