Question

Tìm x biết

a) 3x + 2( 5 - x ) = 0 b) x ( 2x - 1 ) ( x + 5 ) -( 2x² + 1 ) ( x + 4,5 )= 3,5

c) 3x² - 3x ( x - 2 ) = 36 d) ( 3x²- x + 1) (x-1) = x²(4-3x) = 5 trên 2

Answer 1

\(a,3x+2\left(5-x\right)=0\)

\(\Rightarrow3x+10-2x=0\)

\(\Rightarrow x+10=0\)

\(\Rightarrow x=-10\)

\(b,x\left(2x-1\right)\left(x+5\right)-\left(2x^2+1\right)\left(x+4,5\right)=3,5\)

\(\Rightarrow\left(2x^2-x\right)\left(x+5\right)-\left(2x^2+1\right)\left(x+4,5\right)=3,5\)

\(\Rightarrow2x^3+9x^2-5x-2x^3-9x^2-4,5=3,5\)

\(\Rightarrow-5x-4,5=3,5\)

\(\Rightarrow-5x=8\)

\(\Rightarrow x=-\dfrac{8}{5}\)

\(c,3x^2-3x\left(x-2\right)=36\)

\(\Rightarrow3x^2-3x^2+6x=36\)

\(\Rightarrow6x=36\)

\(\Rightarrow x=6\)

\(d,\left(3x^2-x+1\right)\left(x-1\right)=x^2\left(4-3x\right)=\dfrac{5}{2}\)

\(\Rightarrow3x^3-3x^2-x^2+x+x-1+4x^2-3x^3=\dfrac{5}{2}\)

\(\Rightarrow2x-1=\dfrac{5}{2}\)

\(\Rightarrow2x=\dfrac{7}{2}\)

\(\Rightarrow x=\dfrac{7}{4}\)

Answer 2

a,\(3x+2\left(5-x\right)=0\)

\(3x+10-2x=0\)

\(x+10=0\)

\(x=-10\)

Answer 3

c,\(3x^2-3x\left(x-2\right)=36\)

\(3x^2-3x^2+6x=36\)

\(6x=36\)

\(x=6\)

Answer 4

\(b,x\left(2x-1\right)\left(x+5\right)-\left(2x^2+1\right)\left(x+4,5\right)=3,5\)

\(\Rightarrow\left(2x^2-x\right)\left(x+5\right)-\left(2x^2+1\right)\left(x+4,5\right)=3,5\)

\(\Rightarrow2x^3+9x^2-5x-2x^3-9x^2-x-4,5=3,5\)

\(\Rightarrow-6x-4,5=3,5\)

\(\Rightarrow-6x=8\)

\(\Rightarrow x=-\dfrac{4}{3}\)