已知有理数m,n满足(m+n)²=9,(m-n)²=1.求(1)mn (2)m²+n²-mn
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已知有理数m,n满足(m+n)²=9,(m-n)²=1.求(1)mn (2)m²+n²-mn
已知有理数m,n满足(m+n)²=9,(m-n)²=1.求(1)mn (2)m²+n²-mn
已知有理数m,n满足(m+n)²=9,(m-n)²=1.求(1)mn (2)m²+n²-mn
(1) (m+n)^2=9.(1)
(m-n)^2=1.(2)
(1)-(2):(m+n+m-n)(m+n-(m-n))=8
2m*2n=8
mn=2
(2) (m+n)^2=9
m^2+n^2+2mn=9
m^2+n^2-mn=9-3mn=9-3*2=3