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Prove polynomial identities

Is the following proof valid? If not, what is the invalid step in the proof?
    x(9x+3)+3(x+3)~~~~x(9x+3)+3(x+3)
Step 11=9x2+6x+9=9x^2+6x+9
Step 22=(3x+3)2=(3x+3)^2
Step 33=(3(x+1))2=(3(x+1))^2
Step 44=9(x+1)2=9(x+1)^2
Choose 1 answer:
Choose 1 answer: