Question

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

Answer 1

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When x = 3 :

$3 {x}^{3} - 4 {x}^{2} + 7x + 5$

$3 {(3)}^{3} - 4 {(3)}^{2} + 7(3) + 5$

${3}^{4} - 4(9) + 21 + 5$

$81 - 36 + 26$

$71$

When x = - 3 :

$3 {x}^{3} - 4 {x}^{2} + 7x + 5$

$3 {( - 3)}^{3} - 4 {( - 3)}^{2} + 7( - 3) + 5$

$3( - 27) - 4(9) - 21 + 5$

$- 81 - 36 - 16$

$- 133$