Anyone explain how to factorise: 2x^2-7x-15

Question

anonymous · Answer

2x^2-7x-15 = (x-5 )(2x +3).

aroub · Answer

(2x+3)(x-5)

anonymous · Answer

u need to numbers a and b such that
a+b=7/2
ab=-15/2

anonymous · Answer

(a+b)(c+d)=ac+bc+ad+bd

(2x+3)(x-5)=2x^2 +3x -10x -15
                    =2x^2 7x -15

anonymous · Answer

Mark O has a good answer but you need to understand how t o work 'back' from his answer in order to factorise fully.

Multiply the coefficient of x^2 (which is 2) by the constant -15 giving -30
Find  all pairs of factors of -30 then pick the unique pair which add up to -7 (cofficient of x)  (-10 and 3)

Rewrite the equation with -10x and + 3x in place of -7x
2x^2  -10x  + 3x -15
Pair off and bracket...
(2x^2  -10x)  + (3x -15)  now factorise each bracket.
2x(x - 5) +3(x - 5)

The factors are (x - 5) [contents of both brackets]
(2x + 3) [the remaining elements outside brackets]

Answer = (x - 5)(2x + 3)

anonymous · Answer

Thank you very much "gianfranco", is what I neeeded. Appreciate it :)

anonymous · Answer

you are more than welcome