4x+3y=15 (1)
2x-y=17 (2)
(1)-(2)
4x+3y-2x+y=15-17
2x+4y=-2
2(x+2y)=-2
x+2y=-1
(x+2y)^2006=(-1)^2006=1
x+y=20 (1)
1.4/100x+3.7/100y=0.625
所以0.014x+0.037y=0.625 (2)
(1)*0.014-(2)
0.014x+0.014y-0.014x-0.037y=20*0.014-0.625
-0.023y=-0.345
y=15
x=20-y=5
x+y=5k (1)
x-y=9k (2)
(1)*5-(2)
5x+5y-x+y=5k*5-9k
4x+6y=16k
2x+3y=8k
2x+3y=6
所以8k=6
k=3/4