Question

How do you solve x^2+11x+18=0 with either quadratic formula. factoring. or squarerooting

Answer 1

I always prefer factoring, if there are simple factors.
There are simple factors here.

x² + 11x + 18 = 0

(x + 2) (x + 9) = 0

The left side is zero if either factor is zero.

First factor:
x + 2 = 0
x = -2

Second factor:
x + 9 = 0
x = -9

 

Answer 2

$quadratic\ formula:\\\\x^2+11x+18=0\\\\a=1;\ b=11;\ c=18\\\\\Delta=b^2-4ac;\ \Delta=11^2-4\cdot1\cdot18=121-72=49\\\\x_1=\frac{-b-\sqrt\Delta}{2a}\to x_1=\frac{-11-\sqrt{49}}{2\cdot1}=\frac{-11-7}{2}=\frac{-18}{2}=-9\\\\x_2=\frac{-b+\sqrt\Delta}{2a}\to x_2=\frac{-11+7}{2\cdot1}=\frac{-4}{2}=-2$