`1a)` \(\begin{cases}4x+7y=18\\3x-y=1\\\end{cases}\)
`<=>` \(\begin{cases}4x+7y=18\\21x-7y=7\\\end{cases}\)
`<=>` \(\begin{cases}25x=25\\3x-y=1\\\end{cases}\)
`<=>` \(\begin{cases}x=1\\y=3x-1=2\\\end{cases}\)
Vậy hpt có nghiệm `(x,y)=(1,2)`
`b)P=(1/sqrtx+\sqrtx^2/(sqrtx+1)):\sqrtx/(x+sqrtx)`
`đk:x>0`
`P=((sqrtx+1+sqrtx^2)/(sqrtx+x)):\sqrtx/(sqrtx(sqrtx+1))`
`=((x+sqrtx+1)/(sqrtx(sqrtx+1))).(sqrtx+1)`
`=(x+sqrtx+1)/sqrtx`
