Question

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

Tìm x để P(x) =-3

Answer 1

P(x) = (5x³ - 4x² + 2x - 1) + (3 - x + 4x² - 5x³)

= 5x³ - 4x² + 2x - 1 + 3 - x + 4x² - 5x³

= x + 2

Để P (x) = -3 thì x + 2 = -3 <=> x = -5

Answer 2

Ta có : \(P\left(x\right)=\left(5x^3-4x^2+2x-1\right)+\left(3-x+4x^2-5x^3\right)\)

\(\Rightarrow P\left(x\right)=5x^3-4x^2+2x-1+3-x+4x^2-5x^3\)

\(\Rightarrow P\left(x\right)=\left(5x^3-5x^3\right)+\left(-4x^2+4x^2\right)+\left(2x-x\right)+\left(-1+3\right)\)

\(\Rightarrow P\left(x\right)=x+2\)

\(P\left(x\right)=-3\) \(\Leftrightarrow x+2=-3\)

\(\Leftrightarrow x=-5\)

Vậy : \(x=-5\) để \(P\left(x\right)=-3\)

Answer 3

Ta có : P(x)=(5x3−4x2+2x−1)+(3−x+4x2−5x3)

⇒P(x)=5x3−4x2+2x−1+3−x+4x2−5x3

⇒P(x)=(5x3−5x3)+(−4x2+4x2)+(2x−x)+(−1+3)

⇒P(x)=x+2

P(x)=−3 ⇔x+2=−3

⇔x=−5

Vậy : x=−5 để P(x)=−3