Đáp án:
Giải thích các bước giải:
`a)`
`M(x)=P(x)+Q(x)`
`=x^2+2x-5+x^2-9x+5`
`=(x^2+x^2)+(2x-9x)+(-5+5)`
`=2x^2-7x`
`N(x)=P(x)-Q(x)`
`=x^2+2x-5-x^2+9x-5`
`=(x^2-x^2)+(2x+9x)+(-5-5)`
`=11x-10`
`b)`
`M(x)=0`
`=>2x^2-7x=0`
`=>x(2x-7)=0`
`=>` \(\left[ \begin{array}{l}x=0\\x=\dfrac{7}{2}\end{array} \right.\)
`N(x)=0`
`=>11x-10=0`
`=>11x=10`
`=>x=10/11`
`c)`
`Q(x)-P(x)=-[P(x)-Q(x)]`
mà `P(x)-Q(x)=11x-10`
`->Q(x)-P(x)=-(11x-10)=10-11x`
