sin(5x)cos(2x)-cos(5x)sin(2x)

You should have a list of formulas. Very few can get through trigonometry without it. I recall, in my first trigonometry book, the magic page was Page 89. Without Page 89, few could survive an examination. Find such a list in your materials and hang it from your hat until it soaks in. Paste a copy on your bathroom mirror - maybe one on the refrigerator.

There are six formulas like this. Find them all.

sin(a-b) = sin(a)cos(b)-cos(a)sin(b)

It's not magic. It requires memorization.

I am not being harsh. I am being honest. Listen and learn.

Note: "pie" is for eating. "pi" is for math and Greeks.