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N
11 tháng 12 2018
a)\(\frac{x^3-x}{3x+3}=\frac{x.\left(x^2-1\right)}{3.\left(x+1\right)}=\frac{x.\left(x-1\right).\left(x+1\right)}{3.\left(x+1\right)}=\frac{x.\left(x+1\right)}{3}=\frac{x^2+x}{3}\)
31 tháng 12 2019
a) (2x - 1)(3x + 5) - 2(-4x + 1)2 = 6x2 + 10x - 3x - 5 - 2(16x2 - 8x + 1) = 6x2 - 3x - 5 - 32x2 + 16x - 2 = -26x2 + 13x - 7
b) \(\frac{x^2-16}{4x-x^2}=\frac{\left(x-4\right)\left(x+4\right)}{-x\left(x-4\right)}=-\frac{x+4}{x}\)
c) \(\frac{2x-9}{x^2-5x+6}+\frac{2x+1}{x-3}+\frac{x+3}{2-x}\)
= \(\frac{2x-9}{x^2-2x-3x+6}+\frac{\left(2x+1\right)\left(x-2\right)}{\left(x-3\right)\left(x-2\right)}-\frac{\left(x+3\right)\left(x-3\right)}{\left(x-3\right)\left(x-2\right)}\)
= \(\frac{2x-9+2x^2-3x-2-x^2+9}{\left(x-3\right)\left(x-2\right)}\)
= \(\frac{x^2-x-2}{\left(x-3\right)\left(x-2\right)}\)
= \(\frac{x^2-2x+x-2}{\left(x-3\right)\left(x-2\right)}\)
= \(\frac{\left(x+1\right)\left(x-2\right)}{\left(x-3\right)\left(x-2\right)}=\frac{x+1}{x-3}\)
d) (x - 1)3 - (x + 1)3 + 6(x + 1)(x - 1)
= (x - 1 - x - 1)[(x - 1)2 + (x - 1)(x + 1) + (x + 1)2] + 6(x2 - 1)
= -2(x2 - 2x + 1 + x2 - 1 + x2 + 2x + 1) + 6x2 - 6
= -2(3x2 + 1) + 6x2 - 6
= -6x2 - 2 + 6x2 - 6
= -8
e) (2x + 7)2 - (4x + 14)(2x - 8) + (8 - 2x)2
= (2x + 7)2 - 2(2x + 7)(2x - 8) + (2x - 8)2
= (2x + 7 - 2x + 8)2
= 152 = 225
sắp thi hkì r chỉ jùm vs ik
18 tháng 12 2016
a,\(A=\frac{6x+12}{\left(x+2\right)\left(2x-6\right)}=\frac{6\left(x+2\right)}{2\left(x+2\right)\left(x-3\right)}=\frac{3}{x-3}\)
b, Giá trị của x để phân thức có giá trị bằng (-2) :
\(\frac{3}{x-3}=-2\Rightarrow x=1,5\)
Sửa đề : \(B=\frac{x+3}{x+1}-\frac{2x-1}{1-x}+\frac{x+7}{x^2-1}\)
\(=\frac{x+3}{x+1}+\frac{2x-1}{x-1}+\frac{x+7}{x^2-1}\)
\(=\frac{\left(x+3\right)\left(x-1\right)}{\left(x+1\right)\left(x-1\right)}+\frac{\left(2x-1\right)\left(x+1\right)}{\left(x+1\right)\left(x-1\right)}+\frac{x+7}{\left(x+1\right)\left(x-1\right)}\)
\(=\frac{x^2-x+3x-3+2x^2+2x-x-1+x+7}{\left(x+1\right)\left(x-1\right)}\)
\(=\frac{x^2+4x+3}{\left(x+1\right)\left(x-1\right)}=\frac{\left(x+1\right)\left(x+3\right)}{\left(x+1\right)\left(x-1\right)}=\frac{x+3}{x-1}\)
\(B=\frac{x+3}{x+1}-\frac{2x-1}{1-x}+\frac{x+7}{x^2-1}\)
\(=\frac{x+3}{x+1}+\frac{2x-1}{x-1}+\frac{x+7}{\left(x+1\right)\left(x-1\right)}\)
\(=\frac{\left(x+3\right)\left(x-1\right)}{\left(x+1\right)\left(x-1\right)}+\frac{\left(2x-1\right)\left(x+1\right)}{\left(x+1\right)\left(x-1\right)}+\frac{x+7}{\left(x+1\right)\left(x-1\right)}\)
\(=\frac{x^2+2x-3}{\left(x+1\right)\left(x-1\right)}+\frac{2x^2+x-1}{\left(x+1\right)\left(x-1\right)}+\frac{x+7}{\left(x+1\right)\left(x-1\right)}\)
\(=\frac{x^2+2x-3+2x^2+x-1+x+7}{\left(x+1\right)\left(x-1\right)}\)
\(=\frac{3x^2+4x+3}{\left(x+1\right)\left(x-1\right)}\)