\(a,\left(3x-5\right)\left(7-5x\right)-\left(5x+2\right)\left(2-3x\right)=4\)
\(\Leftrightarrow21x-15x^2-35+25x-10x+15x^2-4+6x=4\)
\(\Leftrightarrow42x-43=0\)
\(\Leftrightarrow x=\frac{43}{42}\)
\(b,\left(x+2\right)\left(x^2-2x+4\right)-\left(x^3+3\right)x=14\)
\(\Leftrightarrow x^3+8-x^4-3x=14\)
\(\Leftrightarrow-x^4+x^3-3x-6=0\)( vô nghiệm)
Vậy \(x\in\varnothing\)
a, \((3x-5).(7-5x)-(5x+2).(2-3x)=4\)
\(21x-15x^2-35+25x-[10x-15x^2+4-6x]=4\)
\(21x-15x^2-35+25x-10x+15x^2-4+6x=4\)
\(42x-39=4\)
\(42x=43\)
=> \(x=43/42\)
b, \((x+2).(x^2-2x+4)-(x^3+3).x = 14\)
\(x^3-2x^2+4x+2x^2-4x+8-[x^4+3x]=14\)
\(x^3-2x^2+4x+2x^2-4x+8-x^4-3x=14\)
\(x^3+8-x^4-3x =14 \)
\(-x^4+x^3-3x+8=14\)
\(-x^4+x^3-3x-6=0 ( vô nghiệm ) \)
=> x ∈ ∅
