\(\begin{array}{l} a)3x - 1 = x + 3\\ \Leftrightarrow 3x - x = 3 + 1\\ \Leftrightarrow 2x = 4\\ \Leftrightarrow x = 2\\ b)15 - 7x = 9 - 3x\\ \Leftrightarrow - 7x + 3x = 9 - 15\\ \Leftrightarrow - 4x = - 6\\ \Leftrightarrow x = \dfrac{3}{2}\\ c)x - 3 = 18\\ \Leftrightarrow x = 18 + 3\\ \Leftrightarrow x = 21 \end{array}\)
\(\begin{array}{l} d)2x + 1 = 15 - 5x\\ \Leftrightarrow 2x + 5x = 15 - 1\\ \Leftrightarrow 7x = 14\\ \Leftrightarrow x = 2\\ e)3x - 2 = 2x + 5\\ \Leftrightarrow 3x - 2x = 5 + 2\\ \Leftrightarrow x = 7\\ f) - 4x + 8 = 0\\ \Leftrightarrow - 4x = - 8\\ \Leftrightarrow x = 2 \end{array}\)
Anh sửa đề câu cuối.
\(\begin{array}{l} g)4x + 5 = 3x\\ \Leftrightarrow 4x - 3x = - 5\\ \Leftrightarrow x = - 5\\ h)3 + 2.25 + 2.6 = 2x + 5.0,4x\\ \Leftrightarrow 3 + 50 + 12 = 2x + 2x\\ \Leftrightarrow 47 = 4x\\ \Leftrightarrow x = \dfrac{{47}}{4}\\ i)2x{\left( {x + 2} \right)^2} - 8{x^2} = 2\left( {{x^3} - 8} \right)\\ \Leftrightarrow 2{x^3} + 8{x^2} + 8x - 8{x^2} = 2{x^3} - 16\\ \Leftrightarrow 8x = - 16\\ \Leftrightarrow x = - 2 \end{array}\)
\(a.3x-1=x+3\\\Leftrightarrow 3x-x=1+3\\ \Leftrightarrow2x=4\\ \Leftrightarrow x=2\)
\(b.15-7x=9-3x\\ \Leftrightarrow-7x+3x=-15+9\\\Leftrightarrow -4x=-6\\\Leftrightarrow x=\frac{3}{2}\)
\(c.x-3=18\\\Leftrightarrow x=21\)
\(d.2x+1=15-5x\\ \Leftrightarrow2x+5x=-1+15\\ \Leftrightarrow7x=14\\ \Leftrightarrow x=2\)
\(e.3x-2=2x+5\\ \Leftrightarrow3x-2x=2+5\\ \Leftrightarrow x=7\)
\(f.-4x+8=0\\\Leftrightarrow -4x=-8\\\Leftrightarrow x=2\)
\(g.4x+5=3x\\ \Leftrightarrow4x-3x=5\\\Leftrightarrow x=5\)
\(h.3+2,25+2,6=2x+5+0,4x\\ \Leftrightarrow3+2,25+2,6-5=2,4x\\\Leftrightarrow 2,85=2,4x\\ \Leftrightarrow x=1,1875\)
\(i.2x\left(x+2\right)^2-8x^2=2\left(x-2\right)\left(x^2+2x+4\right)\\ \Leftrightarrow2x\left(x^2+4x+4\right)-8x^2=2\left(x^3-8\right)\\ \Leftrightarrow2x^3+8x^2+8x-8x^2-2x^3=-16\\\Leftrightarrow 8x=-16\\\Leftrightarrow x=-2\)
Mạn phép sửa đề câu \(i\) nhé tiểu cô nương :D