解方程,解出下类方程{x+y+z=100,{70%x+90%y+50%z=78,{80%x+60%y+70%z=69

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解方程,解出下类方程{x+y+z=100,{70%x+90%y+50%z=78,{80%x+60%y+70%z=69
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解方程,解出下类方程{x+y+z=100,{70%x+90%y+50%z=78,{80%x+60%y+70%z=69
解方程,解出下类方程
{x+y+z=100,
{70%x+90%y+50%z=78,
{80%x+60%y+70%z=69

解方程,解出下类方程{x+y+z=100,{70%x+90%y+50%z=78,{80%x+60%y+70%z=69
x+y+z=100 (1)
0.7x+0.9y+0.5z=78 (2)
0.8x+0.6y+0.7z=69 (3)
(1)*0.7-(2):-0.2y+0.2z=-8 (4)
(1)*0.8-(3):0.2y+0.1z=11 (5)
(4)+(5):0.3z=3 z=10
代入(5):y=50
代入(1):x=40
即:x=40,y=50,z=10.

x=320/3;y=50/3;z=-70/3