How do you factor the expression #x^2+4x-21#?

2 Answers
Mar 6, 2018

Answer:

#(x+7)(x-3)#

Explanation:

To factorise any quadratic polynomial , you could use 2 methods.
Here's the easy one
Let the quadratic polynomial be #ax^2+bx+c#

▪multiply #a" and "c# , then factorise the result into some factors, say y and z, #y+z=|b|#
#x^2+4x-21# #(a×c=-21=-3×7)#

#x^2+7x-3x-21#

#x (x+7)-3 (x+7)#

#(x+7)(x-3)#

The other method is a direct application of quadratic formula.

Mar 6, 2018

Answer:

the answer is #(x+7)(x-3)#

Explanation:

there's an easier way to find this but only when it's #x^2#. since you know that two numbers have to multiply to give you #-21# and add to give you #4# when you find it, you don't have to go through the whole process and you can just put them in the parenthesis since there's no number in front of #x#