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2a-b=7.................(1)
(2a-b)²+(a+3b)²=7²..........(2)
(1)代入(2),得
7²+(a+3b)²=7²
(a+3b)²=0
a+3b=0........(2)
(1)*3+(2),得
7a=21
a=3
代入(1),得
2*3-b=7
6-b=7
b=-1
所以
a=3
b=-1

2a-b=7 ,b=2a-7
(2a-b)²+(a+3b)²=7²
7^2+(a+3b)²=7²
(a+3b)²=0
a=-3b
b=2(-3b)-7=-6b-7
7b=-7
b=-1
a=-3b=3

7²+(a+3b)=7²
a+3b=0