Question

Question 7
Find the value of the polynomial $3x^3–4x^2+7x–5$, when x = 3 and also when x = -3.

Answer 1

Let $p\left(x\right)=3x^3–4x^2+7x–5$
At $x=3,p\left(3\right)=3(3{)}^3–4(3{)}^2+7\left(3\right)–5$
$=3\times 27–4\times 9+21–5$
$=81–36+21–5$
$\therefore p\left(3\right)=61$
At $x=-3,p(-3)=3(-3{)}^3–4(-3{)}^2+7(-3)–5$
$=3(-27)–4\times 9–21–5$
$=-81–36–21–5=-143$
$p(-3)=-143$.
Hence, the value of the given polynomial at x = 3 and x = -3 are 61 and -143 respectively.