How do you solve #x^2 + 2x - 15 = 0 #?

2 Answers
Apr 12, 2018

Answer:

#x=-5" or "x=3#

Explanation:

#"the factors of - 15 which sum to + 2 are + 5 and - 3"#

#rArr(x+5)(x-3)=0#

#"equate each factor to zero and solve for x"#

#x+5=0rArrx=-5#

#x-3=0rArrx=3#

Apr 12, 2018

Answer:

#x=-5 or 3#

Explanation:

Rules for factorising:

  • #ax^2+bx+c=0#
  • #m xx n = c#
  • #m + n = b#
  • #:.(x+m)(x+n) = 0#

In this case:

#5 xx -3 = -15 = c#

#5 + -3 = 2 = b#

#:. x^2+2x−15=0 -> color(red)((x+5)(x-3) = 0)#

Either of the brackets must be equal to 0.

Assuming (x+5) = 0:

#color(red)(x=-5)#

Assuming (x-3) = 0:

#color(red)(x=3)#