x+y=600 0.18x+0.21y=120 GIẢI HỆ

Lời giải chi tiết:

`{(x+y=600),(0,18x+0,21y=120):}`

`<=> {(x+y=600),(18/100x+21/100y=120):}`

`<=> {(x+y=600),(100(18/100x+21/100y)=12000):}`

`<=> {(x+y=600),(18x+21y=12000):}`

`<=> {(18(x+y)=10800),(18x+21y=12000):}`

`<=> {(18x+18y=10800),(18x+21y=12000):}`

`<=> {(18x+21y-18x-18y=12000-10800),(18x+21y=12000):}`

`<=> {(3y=1200),(18x+21y=12000):}`

`<=> {(y=400),(18x+21.400=12000):}`

`<=> {(y=400),(18x+8400=12000):}`

`<=> {(y=400),(18x=3600):}`

`<=> {(y=400),(x=200):}`

Vậy hệ phương trình có nghiệm `(x,y)=(200;400)`

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