(2)Y=C+I+G+(X-M)
Y=200+0.8(Y-100)+500+600+[750-(50+0.1Y)]
Y=200+0.8Y-80+500+600+750-50-0.1Y
Y=0.7Y+1920
0.3Y=1920
Y1=6400
政府購買增加至700
Y=200+0.8Y-80+500+700+750-50-0.1Y
Y=0.7Y+2020
0.3Y=2020
Y2=6733
Kg=(6733-6400)/(700-600)
=333/100
=3.33
(3)Y=C+I+G+(X-M)
Y=200+0.8(Y-0)+500+600+750-50-0.1Y
Y=200+0.8Y+500+600+750-50-0.1Y
Y=0.7Y+2000
0.3Y=2000
Y=6667
Kf=(6667-6400)/(0-100)
=-2.67