Q9 of 65 Page 135

Let us factorise the following polynomials:

2x3 – x2 + 9x + 5

Given, f(x)= 2x3 – x2 + 9x + 5

In f(x) putting x=±1, , ±2, ±3, we see for which value of x, f(x)=0


f(−)=2.(− )3−(−)2−9.(− )+5=0


We observe that f(−) = 0


From factor theorem, we can say, for (x=−), (2x+1) is a factor of f(x)


2x3 – x2 + 9x + 5 = 2x3 – x2 + 9x + 5


= 2x3+x2−2x2− x + 10x +5
= x2(2x+1)−x(2x+1)+5(2x+1)


= (2x+1)(x2−x+5)


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