\(0,4x^2-4x-1200=0\)

\(x^2-10x-3000=0\)

\(x^2+50x-60x-3000=0\)

\(x\left(x+50\right)-60x\left(x+50\right)=0\)

\(\left(x+50\right)\left(x-60\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}x=-50\\x=60\end{matrix}\right.\)

PS: Ở bước hai là nhân cả hai vế với 2,5 nhé :)

a, (-0,4x-2)0(1.5x+1)-(-4x-0.8)=3.6
<=>-0,4x-2-1,5x-1+4x+0.8=3,6
<=>2,1x+2,2=3,6
<=>2,1x=1,4
<=>x=2/3

\(\begin{array}{l} a)3x - 1 = x + 3\\ \Leftrightarrow 3x - x = 3 + 1\\ \Leftrightarrow 2x = 4\\ \Leftrightarrow x = 2\\ b)15 - 7x = 9 - 3x\\ \Leftrightarrow - 7x + 3x = 9 - 15\\ \Leftrightarrow - 4x = - 6\\ \Leftrightarrow x = \dfrac{3}{2}\\ c)x - 3 = 18\\ \Leftrightarrow x = 18 + 3\\ \Leftrightarrow x = 21 \end{array}\)

\(\begin{array}{l} d)2x + 1 = 15 - 5x\\ \Leftrightarrow 2x + 5x = 15 - 1\\ \Leftrightarrow 7x = 14\\ \Leftrightarrow x = 2\\ e)3x - 2 = 2x + 5\\ \Leftrightarrow 3x - 2x = 5 + 2\\ \Leftrightarrow x = 7\\ f) - 4x + 8 = 0\\ \Leftrightarrow - 4x = - 8\\ \Leftrightarrow x = 2 \end{array}\)

Anh sửa đề câu cuối.

\(\begin{array}{l} g)4x + 5 = 3x\\ \Leftrightarrow 4x - 3x = - 5\\ \Leftrightarrow x = - 5\\ h)3 + 2.25 + 2.6 = 2x + 5.0,4x\\ \Leftrightarrow 3 + 50 + 12 = 2x + 2x\\ \Leftrightarrow 47 = 4x\\ \Leftrightarrow x = \dfrac{{47}}{4}\\ i)2x{\left( {x + 2} \right)^2} - 8{x^2} = 2\left( {{x^3} - 8} \right)\\ \Leftrightarrow 2{x^3} + 8{x^2} + 8x - 8{x^2} = 2{x^3} - 16\\ \Leftrightarrow 8x = - 16\\ \Leftrightarrow x = - 2 \end{array}\)

\(\frac{3}{5}x+\frac{2}{5}x+\frac{x}{3}=2\)

\(x+\frac{x}{3}=2\)

\(\frac{4}{3}x=2\)

\(x=2:\frac{4}{3}=\frac{3}{2}\)

\(60\%x+0,4.x+\frac{x}{3}=2\)

\(\frac{3}{5}.x+\frac{2}{5}.x+\frac{1}{3}.x=2\)

\(x.\left(\frac{3}{5}+\frac{2}{5}+\frac{1}{3}\right)=2\)

\(x.\frac{4}{3}=2\)

\(x=2:\frac{4}{3}\)

\(x=\frac{3}{2}=1,5\)

60% x + 0,4x + x : 3 = 2

3/5 . x + 2/5 . x + x : 3 = 2

(3/5 + 2/5) x + x : 3 = 2

x + x : 3 = 2

x : (1 + 3) = 2

x : 4 = 2

x = 8

60% x + 0,4 x + x : 3 = 2

3/5 . x + 2/5 . x + x : 3 = 2

x . ( 3/5 + 2/5 ) + x : 3 =2

x . ( 1+ 1/3) = 2

x . 4/3 = 2

x = 2 : 4/3

x = 3/2

lưu ý : dấu / là dấu phần

dấu . là dấu nhân

\(P=\dfrac{\sqrt{x}}{\sqrt{x}+3}:\dfrac{2\sqrt{x}}{\sqrt{x}-3}-\dfrac{3x+9}{x-9}\)

\(=\dfrac{\sqrt{x}-3}{2\left(\sqrt{x}+3\right)}-\dfrac{3x+9}{x-9}\)

\(=\dfrac{x-9-3x-9}{2\left(x-9\right)}=\dfrac{-2x-18}{2\left(x-9\right)}=\dfrac{-x-9}{x-9}\)

đề là -4x² ạ

\(-27x^2+257-1200=-\left(3\sqrt{2}x-\dfrac{256}{6\sqrt{3}}\right)^2-\dfrac{16016}{27}< 0\forall x\)

\(\Rightarrow\) phương trình vô nghiệm