x³ - 30x² - 31x -1
=x³ + ( 1 - 31)x² - 31 x - 1
= (x³ +x²) - (31x² + 31x) - 1
= x²(x+1) - 31x (x+1) - 1
=(x² - 31x)(x+1 )- 1
=x(x-31)(x+1) - 1
=31 . 0 . 32 - 1 = -1 (thay x =31)
$x^{5}$ - $15x^{4}$ + $16x^{3}$ - $29x^{2}$ +13
= $x^{5}$ + $x^{4}$ - $16x^{4}$ + $16x^{3}$ - $16x^{2}$ - $13x^{2}$ +13
= -x² +13 vì các tổng trong ngoặc =0
=-196 +13 = -183
