Question

Factor completely: 2a^2 - a - 10

Answer 1

(2a-5)(a+2)

Answer 2

This is different case :D , for a polynomial of the form ax^(2)+bx+c, find two factors of a*c (-20) that add up to b (-1).

In this problem 2*-(5)/(2)=-(10)/(2) (which is (c)/(a)) and 2-(5)/(2)=-(1)/(2) (which is ((b)/(a)) ,

so insert 2 as the right hand term of one factor and -(5)/(2) as the righthand term of the other factor.
(a+2)(a-(5)/(2))

remove the fraction by multiplying the first term of the factor by the denom of the second term
(a+2)(2a-5)

Get it?