用代入法解下列方程组 (1)x=6-5y,3x-6y=4; (2)5x+2y=15,x+y=6; (3)3x+4y=2,2x-y=5; 2x+3y=7,2x-y=5
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![用代入法解下列方程组 (1)x=6-5y,3x-6y=4; (2)5x+2y=15,x+y=6; (3)3x+4y=2,2x-y=5; 2x+3y=7,2x-y=5](/uploads/image/z/93620-20-0.jpg?t=%E7%94%A8%E4%BB%A3%E5%85%A5%E6%B3%95%E8%A7%A3%E4%B8%8B%E5%88%97%E6%96%B9%E7%A8%8B%E7%BB%84+%281%29x%3D6-5y%2C3x-6y%3D4%3B+%282%295x%2B2y%3D15%2Cx%2By%3D6%3B+%283%293x%2B4y%3D2%2C2x-y%3D5%3B+2x%2B3y%3D7%2C2x-y%3D5)
用代入法解下列方程组 (1)x=6-5y,3x-6y=4; (2)5x+2y=15,x+y=6; (3)3x+4y=2,2x-y=5; 2x+3y=7,2x-y=5
用代入法解下列方程组 (1)x=6-5y,3x-6y=4; (2)5x+2y=15,x+y=6; (3)3x+4y=2,2x-y=5; 2x+3y=7,2x-y=5
用代入法解下列方程组 (1)x=6-5y,3x-6y=4; (2)5x+2y=15,x+y=6; (3)3x+4y=2,2x-y=5; 2x+3y=7,2x-y=5
x=6-5y.1
3x-6y=4.2
将1式代入2式得
3(6-5y)-6y=4
18-15y-6y=4
18-21y=4
21y=18-4
21y=14
y=2/3
x=6-5y=6-5*2/3=8/3
5x+2y=15.1
x+y=6.2
由2式得
x=6-y.3
将3式代入1式得
5(6-y)+2y=15
30-5y+2y=15
30-3y=15
3y=30-15
3y=15
y=5
x=6-y=6-5=1
3x+4y=2.1
2x-y=5.2
由2式得
y=2x-5.3
将3式代入1式得
3x+4(2x-5)=2
3x+8x-20=2
11x=20+2
11x=22
x=2
y=2x-5=2*2-5=-1
2x+3y=7.1
2x-y=5.2
由2式得
y=2x-5.3
将3式代入1式得
2x+3(2x-5)=7
2x+6x-15=7
8x=15+7
8x=22
x=11/4
y=2x-5=2*11/4-5=1/2
(1)因x=6-5y及为3(6-5y)-6y=4 (2)由条件可知x=6-y所以
18-15y=4
-15y=4-18
y=-14/-15
y=14/15
所以x=4/3
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