1)
\(M+\left(5x^2-2xy\right)=6x^2+9xy-y^2\)
\(M+5x^2-2xy=6x^2+9xy-y^2\)
\(M=\left(6x^2+9xy-y^2\right)-\left(5x^2+2xy\right)\)
\(M=6x^2+9xy-y^2-5x^2-2xy\)
\(M=\left(6x^2-5x^2\right)+\left(9xy-2xy\right)-y^2\)
\(M=x^2+7xy-y^2.\)
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