algebra precalculus - Significance of transforming the left side into the right?

I have a math problem that asks:

Use trig identities to transform the left side of the equation into the right side: $\cos\theta \sec\theta = 1$

I'm having trouble with this concept since my teacher doesn't explain well what value this operation would have. I can get to the answer but I don't understand the steps and why I'm doing it. What's the significance?

Answer

In general, trigonometric identities are interesting for their own sake. In this case, it is a simple matter of applying definitions. We have $\cos\theta\sec\theta=\cos\theta\frac{1}{\cos\theta}=1$. We are trying to show that the two sides are equal and one way is to work from left to right.