giúp mik đi ạ
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3:
a: =>2x^2+8x-3x-12>2x^2+2
=>5x>14
=>x>14/5
b: =>3(3x-1)-2(5x+1)>4*3*2=24
=>9x-3-10x-2>24
=>-x-5>24
=>x+5<-24
=>x<-29
4:
Gọi vận tốc thật của cano là x
Theo đề, ta có phương trình:
5(x+2)=6(x-2)
=>5x+10=6x-12
=>-x=-22
=>x=22
Độ dài quãng đường là 5(22+2)=120km
a: \(=\dfrac{2x^3+x^2-6x^2-3x+2x+1}{2x+1}=2x^2-3x+1\)
b: \(=\dfrac{x^3+2x^2-2x^2-4x+2x+4}{x+2}=x^2-2x+2\)
d: \(=\dfrac{\left(x^2-1\right)\left(x^2+1\right)-2x\left(x^2-1\right)}{x^2-1}=\left(x-1\right)^2\)
h: \(=\dfrac{x^3+x^2-3x^2-3x+8x+8}{x+1}=x^2-3x+8\)
\(c,\)
\(\left(6x^3-19x^2+23x-12\right):\left(2x-3\right)\)
\(=\left(6x^3-10x^2-9x^2+8x+15x-12\right):\left(2x-3\right)\)
\(=\left[\left(6x^3-10x^2+8x\right)-\left(9x^2-15x+12\right)\right]:\left(2x-3\right)\)
\(=\left[2x\left(3x^2-5x+4\right)-3\left(3x^2-5x+4\right)\right]:\left(2x-3\right)\)
\(=\left[\left(3x^2-5x+4\right)\left(2x-3\right)\right]:\left(2x-3\right)\)
\(=3x^2-5x+4\)
\(e,\)
\(\left(6x^3-5x^2+4x-1\right):\left(2x^2-x+1\right)\)
\(=\left(6x^3-3x^2-2x^2+3x+x-1\right):\left(2x^2-x+1\right)\)
\(=\left[\left(6x^3-3x^2+3x\right)-\left(2x^2-x+1\right)\right]:\left(2x^2-x+1\right)\)
\(=\left[3x\left(2x^2-x+1\right)-\left(2x^2-x+1\right)\right]:\left(2x^2-x+1\right)\)
\(=\left[\left(2x^2-x+1\right)\left(3x-1\right)\right]:\left(2x^2-x+1\right)\)
\(=3x-1\)
\(f,\)
\(\left(x^3-2x^2-5x+6\right):\left(x+2\right)\)
\(=\left(x^3-4x^2+2x^2+3x-8x+6\right):\left(x+2\right)\)
\(=\left[\left(x^3+2x^2\right)-\left(4x^2+8x\right)+\left(3x+6\right)\right]\)
\(=\left[x^2\left(x+2\right)-4x\left(x+2\right)+3\left(x+2\right)\right]\)
\(=\left[\left(x+2\right)\left(x^2-4x+3\right)\right]:\left(x+2\right)\)
\(=x^2-4x+3\)
\(g,\)
\(\left(x^3-2x^2-5x+6\right):\left(x+2\right)\)
\(=\left(x^3+2x^2-4x^2-8x+3x+6\right):\left(x+2\right)\)
\(=\left[\left(x^3+2x^2\right)-\left(4x^2+8x\right)+\left(3x+6\right)\right]:\left(x+2\right)\)
\(=\left[x^2\left(x+2\right)-4x\left(x+2\right)+3\left(x+2\right)\right]:\left(x+2\right)\)
\(=\left[\left(x+2\right)\left(x^2-4x+3\right)\right]:\left(x+2\right)\)
\(=x^2-4x+3\)
Bài 1:
a: 3/5+4/9=27/45+20/45=47/45
Bài 4:
a: =1/5+1/6+5/8=24/120+20/120+75/120=119/120
b: =8/12+2/12+5/12=15/12=5/4
a)\(\dfrac{1}{5}+\dfrac{1}{6}+\dfrac{5}{8}=\dfrac{24}{120}+\dfrac{20}{120}+\dfrac{75}{120}=\dfrac{119}{120}\)
b)\(\dfrac{8}{12}+\dfrac{2}{12}+\dfrac{5}{12}=\dfrac{15}{12}=\dfrac{5}{4}\)