0.8x-1.7y=-7 …① 5x-3y=2 …②还有个.5分之2x-1 + 4分之3y-2=0 (1)5分之3x+1 - 4分之3y+2=0 (2)
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0.8x-1.7y=-7 …① 5x-3y=2 …②还有个.5分之2x-1 + 4分之3y-2=0 (1)5分之3x+1 - 4分之3y+2=0 (2)
0.8x-1.7y=-7 …① 5x-3y=2 …②
还有个.
5分之2x-1 + 4分之3y-2=0 (1)
5分之3x+1 - 4分之3y+2=0 (2)
0.8x-1.7y=-7 …① 5x-3y=2 …②还有个.5分之2x-1 + 4分之3y-2=0 (1)5分之3x+1 - 4分之3y+2=0 (2)
0.8x-1.7y=-7(1)
5x-3y=2(2)
(1)*50-(2)*8
40x-85y-40x+24y=-350-16
-61y=-366
y=6
x=4
两边乘20
8x+15y=14(1)
12x-15y=6(2)
相加
20x=20
x=1,y=2/5
a+1/a=3
两边平方得
a^2+1/a^2+2=9
a^2+1/a^2=7
a^2+1/a^2-2=7-2
(a-1/a)^2=5
a-1/a=±√5
a^2-1/a^2=(a+1/a)(1-1/a)=3×±√5=±3√5