Giải hệ P/T $\begin{cases} x+y=720\\\dfrac{115}{100}x+ \dfrac{112}{100}y = 819 \end{cases}$
1 câu trả lời
`{(x+y=720),(\frac{115}{100}x+\frac{112}{100}y=819):}`
`⇔{(x+y=720),(\frac{1}{100}(115x+112y)=819):}`
`⇔{(x+y=720),(115x+112y=81900):}`
`⇔{(112x+112y=80640),(115x+112y=81900):}`
`⇔{(3x=1260),(115x+112y=81900):}`
`⇔{(x=420),(115.420+112y=81900):}`
`⇔{(x=420),(y=300):}`
Vậy hệ ptr đã cho có nghiệm`(x;y)=(420;300)`