Question

Giải hệ phương trình sau

\(x+y=140\)

 \(x-\frac{x}{8}=y+\frac{8}{x}\)

Answer 1

Ta có: x + y = 140 => x = 180 - y

Thay x = 180 - y vào x - x/8 = y + 8/x ta đc:

\(180-y-\frac{180-y}{8}=y+\frac{8}{180-y}\)

\(\Rightarrow\left(180-y\right)\left(180-y\right).8-\left(180-y\right)\left(180-y\right)=8y\left(180-y\right)+8.8\)

\(\Rightarrow\left(180-y\right)^2.8-\left(180-y\right)^2=8y\left(180-y\right)+64\)

\(\Rightarrow\left(32400-360y+y^2\right).8-\left(32400-360y+y^2\right)=1440y-8y^2+64\)

\(\Rightarrow259200-2880y+8y^2-32400+360y-y^2-1440y+8y^2-64=0\)

\(\Rightarrow15y^2-3960y+226736=0\)

\(\Rightarrow y=180\) hoặc y = 84

Khi y = 180 => x = 0

Khi y = 84 => x = 96

Answer 2

hình như tớ lm lộn rồi :v , thui kệ đi ..... mệt