Đáp án:
`S={(+-sqrt2081-41)/2}`
Giải thích các bước giải:
`4x(x+41)=400`
`<=>x(x+41)=100`
`<=>x^2+41x-100=0`
`<=>x^2+41+1681/4-2081/4=0`
`<=>(x+41/2)^2=2081/4=(±(sqrt2081)/2)^2`
`<=>` \(\left[ \begin{array}{l}x+\dfrac{41}2=\dfrac{-\sqrt{2081}}2\\x+\dfrac{41}2=\dfrac{\sqrt{2081}}2\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=\dfrac{-\sqrt{2081}-41}2\\x=\dfrac{\sqrt{2081}-41}2\end{array} \right.\)
Vậy `S={(+-sqrt2081-41)/2}`
