Consider the derivation of sin(2x).

Where is the error?

Step 2 should read = cos(x)cos(x) – sin(x)sin(x).
Step 2 should read = sin(x)cos(x) – cos(x)sin(x).
Step 3 should read = – 2sin(x)cos(x).
Step 3 should read = 2sin(x)cos(x).