Question

[Phạm Đỗ Bảo Ngọc]

bài 49; tìm x

1, x mũ 3 + 3x mũ 2 - ( x + 3 )

2, 15x - 5 + 6x mũ 2 - 2x = 0

3, 5x - 2 - 25x mũ 2 + 10x = 0

Answer 1

[Nguyễn Huy Tú]

a, \(x^3+3x^2-\left(x+3\right)=0\Leftrightarrow x^2\left(x+3\right)-\left(x+3\right)=0\)

\(\Leftrightarrow\left(x-1\right)\left(x+1\right)\left(x+3\right)=0\Leftrightarrow x=1;x=-1;x=-3\)

b, \(15x-5+6x^2-2x=0\Leftrightarrow5\left(3x-1\right)+2x\left(3x-1\right)=0\)

\(\Leftrightarrow\left(2x+5\right)\left(3x-1\right)=0\Leftrightarrow x=-\frac{5}{2};x=\frac{1}{3}\)

c, \(5x-2-25x^2+10x=0\)

\(\Leftrightarrow\left(5x-2\right)-5x\left(5x-2\right)=0\Leftrightarrow\left(1-5x\right)\left(5x-2\right)=0\Leftrightarrow x=\frac{2}{5};x=\frac{1}{5}\)

Answer 2

[Đặng Hữu Thành Đạt]

= 1/5 nha