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b)(2x - 1)^2 - (2x + 5) (2x - 5 ) = 18
4x 2 -4x+1-4x 2+25=18
26-4x=18
4x=8
x=2
a,27x-18=2x-3x^2
<=> 3x^2-2x+27-18x=0
<=> 3x^2-20x+27=0
\(\Delta\)= 20^2-4-12.27
tính \(\Delta\)rồi tìm x1 ,x2
Q = \(\frac{\left(x+2\right)^2}{x}\cdot\left(1-\frac{x^2}{x+2}\right)-\frac{x^2+6x+4}{x}\)
Q = \(\frac{\left(x+2\right)^2}{x}\cdot\frac{x+2-x^2}{x+2}-\frac{x^2+6x+4}{x}\)
Q = \(\frac{\left(x+2\right)\left(x+2-x^2\right)}{x}-\frac{x^2+6x+4}{x}\)
Q = \(\frac{x^2+2x-x^3+2x+4-2x^2-x^2-6x-4}{x}\)
Q = \(\frac{-x^3-2x^2-2x}{x}\)
Q = \(\frac{x\left(-x^2-2x-2\right)}{x}=-x^2-2x-2\)
a) ĐKXĐ: \(x\ne1\)
b) \(A=\frac{2}{x-1}+\frac{2\left(x+1\right)}{x^2+x+1}+\frac{x^2-10x+3}{x^3-1}\)
\(=\frac{2\left(x^2+x+1\right)}{\left(x-1\right)\left(x^2+x+1\right)}+\frac{2\left(x+1\right)\left(x-1\right)}{\left(x-1\right)\left(x^2+x+1\right)}+\frac{x^2-10x+3}{\left(x-1\right)\left(x^2+x+1\right)}\)
\(=\frac{2x^2+2x+2}{\left(x-1\right)\left(x^2+x+1\right)}+\frac{2x^2-2}{\left(x-1\right)\left(x^2+x+1\right)}+\frac{x^2-10x+3}{\left(x-1\right)\left(x^2+x+1\right)}\)
\(=\frac{5x^2-8x+3}{\left(x-1\right)\left(x^2+x+1\right)}=\frac{\left(x-1\right)\left(5x-3\right)}{\left(x-1\right)\left(x^2+x+1\right)}=\frac{5x-3}{x^2+x+1}\)
a) Ta có : (x - 5)2 - 16
= (x - 5)2 - 42
= (x - 5 - 4)(x - 5 + 4)
= (x - 1)(x - 9)
b) 25 - (3 - x)2
= 52 - (3 - x)2
= (5 - 3 + x)(5 + 3 - x)
= (x + 2)(8 - x)
c) (7x - 4)2 - (2x + 1)2
= (7x - 4 - 2x - 1)(7x - 4 + 2x + 1)
= (5x - 5)(9x - 3)
= 5(x - 1)3(3x - 1)
= 15(x - 1)(3x - 1)
\(b,\left(x+2\right)\left(x^2-2x+4\right)-x\left(x^2+2\right)=15\)
\(\Leftrightarrow x^3+8-x^3-2x=15\)
\(\Leftrightarrow-2x=15-8=7\)
\(\Leftrightarrow x=\frac{-7}{2}\)
Vậy \(x=\frac{-7}{2}\)
Đặt \(y=x-1\Rightarrow x=y+1\)
Ta có \(A=\frac{\left(y+1\right)^2+\left(y+1\right)+1}{y^2}=\frac{y^2+3y+3}{y^2}=\frac{3}{y^2}+\frac{3}{y}+1\)
Lại đặt \(t=\frac{1}{y}\) , \(A=3t^2+3t+1=3\left(t+\frac{1}{2}\right)^2+\frac{1}{4}\ge\frac{1}{4}\)
Vậy A đạt giá trị nhỏ nhất bằng 1/4 khi t=-1/2 <=> y = -2 <=> x = -1
thanks bn nha!