\(5x\left(4x^2-2x+1\right)-2x\left(10x^2-5x+2\right)=-36\)

\(5x\times4x^2+5x\times\left(-2x\right)+5x\times1-2x\times10x^2-2x\times\left(-5x\right)-2x\times2=-36\)

\(20x^3-10x^2+5x-20x^3+10x^2-4x=-36\)

\(\left(20x^3-20x^3\right)+\left(-10x^2+10x^2\right)+\left(5x-4x\right)=-36\)

\(x=-36\)

Vậy x= -36.

a) P(x)+Q(x)= ( \(x^4\) -\(5x^3+4x-5\) )+(-\(x^4\) \(+3x^2+2x+1\) )

= \(x^4-5x^3+4x-5-x^4+3x^2+2x+1\)

=( \(x^4-x^4\) ) \(-5x^3\)\(+(4x+2x)+(-5+1)+3x^2\)

=\(-5x^3+6x-4+3x^2\)

=\(-5x^3+3x^2+6x-4\)

b) P(x)=R(x)+Q(x).

R(x)=P(x)-Q(x)

R(x)=( \(x^4-5x^3+4x-5\) ) - ( \(-x^4+3x^2+2x+1)\)

R(x)= \(x^4-5x^3+4x-5+x^4-3x^2-2x-1\)

R(x)=\((x^4+x^4)-5x^3+(4x-2x)+(-5-1)-3x^2\)

R(x)= \(2x^4-5x^3-3x^2+2x\) -6

hay