### Home > CALC > Chapter 5 > Lesson 5.3.3 > Problem 5-135

5-135.

If *y* = (cos *x* + sin *x*)^{2} , find

Method 1: Before you differentiate, expand and simplify using trig identities. Then use the Product Rule to differentiate.

Method 2: Chain Rule.

The results might not look the same. This is where you get to practice proving a trig identity (in other words, proving that the two results are equivalent.)