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# Add & subtract polynomials: find the error

## Problem

Javier tried to subtract two polynomials. His work is shown below:
\begin{aligned} &\phantom{=}(x^4-3x^2y^2+y^4)-(-11x^4+4x^2y^2-3y^4) \\\\ &=x^4-3x^2y^2+y^4+11x^4-4x^2y^2+3y^4&\text{Step }1 \\\\ &=(1-3)x^6+(-3+1)y^6 +(11-4)x^6+(-4+3)y^6&\text{Step }2 \\\\ &=-2x^6-2y^6+7x^6-y^6&\text{Step }3 \end{aligned}
At which step did Javier make an error, if at all?