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Add & subtract polynomials: find the error

Victoria tried to subtract two polynomials. Her work is shown below:
=(7a2+4abb2)(2a23ab+6b2)=7a2+4abb22a23ab+6b2Step 1=(72)a2+(43)ab+(1+6)b2Step 2=5a2+ab+5b2Step 3\begin{aligned} &\phantom{=}(7a^2+4ab-b^2)-(2a^2-3ab+6b^2) \\\\ &=7a^2+4ab-b^2-2a^2-3ab+6b^2&\text{Step }1 \\\\ &=(7-2)a^2+(4-3)ab+(-1+6)b^2&\text{Step }2 \\\\ &=5a^2+ab+5b^2&\text{Step }3 \end{aligned}
At which step did Victoria make an error, if at all?
Choose 1 answer:
Choose 1 answer: