Review the proof of the identity cos(π − A) = −cosA.

cos(π − A)

Step 1: = cosπcosA − sinAsinπ

Step 2: = (−1)(cosA) + (sinA)(0)

Step 3: = −1cosA + (sinA)(0)

Step 4: = −cosA + 0

Step 5: = −cosA

At which step was an error made?

step 1
step 2
step 3
step 4