Đáp án-Giải thích các bước giải:
`M+N=x^2+2xy-4y^2+5^2+2xy+x^2-1`
`M+N=(x^2+x^2)+(2xy+2xy)-4y^2+(5^2-1)`
`M+N=2x^2+4xy-4y^2+24`
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`M-N= x^2 + 2xy - 4y^2-(5^2 + 2xy + x^2 - 1)`
`M-N=x^2+2xy-4y^2-25-2xy-x^2+1`
`M-N=(x^2-x^2)+(2xy-2xy)-4y^2+(-25+1)`
`M-N=-4y^2-24`
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`N-M=5^2 + 2xy + x^2 - 1-( x^2 + 2xy - 4y^2)`
`N-M=25+ 2xy + x^2 - 1-x^2-2xy+4y^2`
`N-M=(x^2-x^2)+(2xy-2xy)+4y^2+(25-1)`
`N-M=4y^2+24`
