若m^2-mn=5,mn-n^2=-4,则m^2-n^2=?,m^2-2mn+n^2=?

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若m^2-mn=5,mn-n^2=-4,则m^2-n^2=?,m^2-2mn+n^2=?

若m^2-mn=5,mn-n^2=-4,则m^2-n^2=?,m^2-2mn+n^2=?
若m^2-mn=5,mn-n^2=-4,则m^2-n^2=?,m^2-2mn+n^2=?

若m^2-mn=5,mn-n^2=-4,则m^2-n^2=?,m^2-2mn+n^2=?
∵m^2-mn=5①
mn-n²=-4②
∴①+②:m²-n²=5-4=1
①-②:m²-2mn+n²=5-(-4)=9

第一个=9,第二个=1

(m^2-mn)+(mn-n^2)=5 +(-4)
去括号得 m^2-n^2=1
(m^2-mn)-(mn-n^2)=5 -(-4)
去括号得 m^2-2mn+n^2=9

m^2-mn+mn-n^2=m^2-n^2=5-4=1
m^2-mn-(mn-n^2)=m^2-2mn+n^2=5+4=9

m^2-mn=5 mn-n^2=-4 两者相加m^2-n^2=1;两者相减m^2-2mn+n^2=9

m^2-mn=5
mn-n^2=-4
相加
m^2-n^2=1
相减
m^2-2mn+n^2=9