Bài 5:
a) \(\left(x+1\right)\left(x^2-x+1\right)-x\left(x-3\right)\left(x+3\right)=-26\)
\(\Rightarrow x\left(x^2-x+1\right)+\left(x^2-x+1\right)-x\left(x^2-9\right)=-26\\ \Rightarrow x^3-x^2+x+x^2-x+1-x^3+9x=-26\\ \Rightarrow9x+1=-26\\ \Rightarrow9x=-27\\ \Rightarrow x=3\)
b) \(4\left(x+1\right)^2+\left(2x-1\right)^2-8\left(x-1\right)\left(x+1\right)=11\)
\(\Rightarrow4\left(x^2+2x+1\right)+4x^2-4x+1-8\left(x^2-1\right)=11\\ \Rightarrow4x^2+8x+4+4x^2-4x+1-8x^2+8=11\\ \Rightarrow4x+13=11\\ \Rightarrow4x=-2\\ \Rightarrow x=-\dfrac{1}{2}\)
c) \(\left(x-2\right)^2-\left(x+3\right)^2-4\left(x+1\right)=5\)
\(\Rightarrow\left(x-2-x-3\right)\left(x-2+x+3\right)-4x-4=5\\ \Rightarrow-5.\left(2x+1\right)-4x-4=5\\ \Rightarrow-10x-5-4x-4=5\\ \Rightarrow-14x-9=5\\ \Rightarrow-14x=14\\ \Rightarrow x=-1\)
d) \(\left(2x-3\right)\left(2x+3\right)-\left(x-1\right)^2-3x\left(x-5\right)=-44\)
\(\Rightarrow4x^2-9-x^2+2x-1-3x^2+15x=-44\\ \Rightarrow17x-10=-44\\ \Rightarrow17x=-34\\ \Rightarrow x=-2\)
