更新时间2019-07-26 15:41:36
∵(m+n)²=9,(m-n)²=1
∴m²+2mn+n²=9①,m²-2mn+n²=1②
①+②得:2m²+2n²=10
∴m²+n²=5
①-②得:4mn=8
∴mn=2
∴m²+n²-mn=5-2=3
1、(m+n)²-(m-n)²=4mn=8
所以mn=2
2、m²+n²-mn=(m-n)²+mn
所以m²+n²-mn=1+2=3
[1]解:
(m+n)²-(m-n)²=m²+2mn+n²-m²+2mn-n²=4mn
4mn=9-1
4mn÷4=8÷4
mn=2
[2]解:
(m+n)²-2mn=m²+n²
m²+n²=9-4
m²+n²=5
m²+n²-mn=5-mn
m²+n²-mn=5-2
(m+n)²=m²+2mn+n²=9①
(m-n)²=m²-2mn+n²=1②
①-②得4mn=9-1
mn=2③
②+③得m²+n²-mn=1+2=3
(m+n)²=9,即m²+2mn+n²=9
(m-n)²=1,即m²-2mn+n²=1
(1)4mn=9-1=8,mn=2
(2)m²+n²-mn=1+2=3