Definite integrals u-substitution

Question

Please may you explain how did we jump from the step 2 to step 3 in the screenshot (provided below).

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Answer 1

You can do this in two ways:

Method 1:

$u=\sec(x) \Rightarrow du = \sec(x)\tan(x)dx$

Method 2:

$$\sec(x)\tan(x)=\frac{1}{\cos(x)}\frac{\sin(x)}{\cos(x)} = \frac{\sin x}{\cos^2(x)}$$

Substitute $u=\cos(x) \Rightarrow du=-\sin(x)dx$

Can you continue from either one?