Bài 5: 

4: ta có: $5x\left(-x+1\right)-5\left(-x^2-x\right)=0$

$\iff -5x\left(x-1\right)+5x\left(x+1\right)=0$

$\iff 5x\left(-x+1+x+1\right)=0$

hay x=0

$H=x^5-70x^4-70x^3-70x^2-70x+29$

$=x^4\left(x-71\right)+x^3\left(x-71\right)+x^2\left(x-71\right)+x\left(x-71\right)+x+29$

$=x^4\left(71-71\right)+x^3\left(71-71\right)+x^2\left(71-71\right)+x\left(71-71\right)+71+29$

$=0+71+29=100$

nhiều thế

$1.2x^2-x-2x^2-5=0$

$-x-5=0\iff x=-5$

$2.-2x^2-x+2x^2-2=0$

$-x-2=0\iff x=-2$

$3.12x^2+3x+24x-12x^2=0$

$27x=0\iff x=0$

$4.-5x^2+5x+5x^2+5x=0$

−10x(2−x)−5x(x+2)=5x(x+3)⇒5x(x+3)+5x(x+2)+10x(2−x)=0⇒5x(x+3+x+2+4−2x)=0⇒5x.9=0⇒45x=0⇒x=0