Question

用代入法解下列方程组.3X+4Y=16 5X-6Y=33 4（X-Y-1)=3(1-Y)-2 X/2+Y/3=2 某班去

Answer 1

3x+4y=16 (1)

5x-6y=33 (2)

由(1)得到x=(16-4y)/3 (3)

代入(2)

5(16-4y)/3-6y=33

80/3-20y/3-6y=33

38y/3=-19/3

y=-1/2

代入(3)

x=(16-4y)/3=6

4（x-y-1)=3(1-y)-2 *1)

x/2+y/3=2 (2)

由(2)得到x=2*(2-y/3) (3)

代入(1)

4[2*(2-y/3)-y-1]=3(1-y)-2

16-8y/3-4y-4=3-3y-2

11y/3=11

y=3

代入(3)

x=2*(2-y/3)=2

设甲票x张,乙票y张

x+y=35 (1)

24x+18y=750 (2)

由(1)得到x=35-y (3)

代入(2)

24(35-y)+18y=750

840-24y+18y=750

6y=90

y=15

x=35-y=20

所以甲票20张,乙票15张