Determine whether given polynomial identities are true, and whether given proofs of such identities are valid.

Problem

Is the following proof valid? If not, what is the invalid step in the proof?
space, space, space, space, left parenthesis, 4, x, minus, 3, right parenthesis, left parenthesis, x, minus, 2, right parenthesis, start superscript, 2, end superscript
Step 1equals, left parenthesis, 4, x, minus, 3, right parenthesis, left parenthesis, x, minus, 2, right parenthesis, left parenthesis, x, minus, 2, right parenthesis
Step 2equals, left parenthesis, 4, x, minus, 3, right parenthesis, left parenthesis, x, start superscript, 2, end superscript, minus, 2, x, minus, 2, x, plus, 4, right parenthesis
Step 3equals, left parenthesis, 4, x, minus, 3, right parenthesis, left parenthesis, x, start superscript, 2, end superscript, minus, 4, x, plus, 4, right parenthesis
Step 4equals, 4, x, start superscript, 3, end superscript, minus, 16, x, start superscript, 2, end superscript, plus, 16, x, minus, 3, x, start superscript, 2, end superscript, minus, 12, x, minus, 12
Step 5equals, 4, x, start superscript, 3, end superscript, minus, 19, x, start superscript, 2, end superscript, plus, 4, x, minus, 12
Please choose from one of the following options.