Question:
Find the value of the polynomial $3 x^{3}-4 x^{2}+7 x-5$, when $x=3$ and also when $x=-3$.
Solution:
Let p(x) =3x3 – 4x2 + 7x – 5
At x= 3, p(3) = 3(3)3 – 4(3)2 + 7(3) – 5
= 3×27-4×9 + 21-5 = 81-36+21-5 P( 3) =61
At x = -3, p(-3)= 3(—3)3 – 4(-3)2 + 7(-3)- 5
= 3(-27)-4×9-21-5 = -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.