Question:
Find the product:
(9x2 − x + 15) × (x2 − x − 1)
Solution:
By horizontal method:
$\left(9 x^{2}-x+15\right) \times\left(x^{2}-x-1\right)$
$=x^{2}\left(9 x^{2}-x+15\right)-x\left(9 x^{2}-x+15\right)-1\left(9 x^{2}-x+15\right)$
$=9 x^{4}-x^{3}+15 x^{2}-9 x^{3}+x^{2}-15 x-9 x^{2}+x-15$
$=9 x^{4}-10 x^{3}+7 x^{2}-14 x-15$
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