How do you find the roots, real and imaginary, of y=-(x+5)^2+2x^2 + 5x - 12 using the quadratic formula?

1 Answer
Jul 11, 2017

x_1~~6.437+0i
x_2~~-1.437+0i

Explanation:

Quadratic formula, given by:
(-b+-sqrt(b^2-4ac))/(2a)

Before we proceed, let's us expand the equation of y
y=-(x+5)^2+2x^2+5x-12
y=-(x^2+10x+25)+2x^2+5x-12
y=-x^2-10x-25+2x^2+5x-12
y=(2-1)x^2+(5-10)x+(-37)
y=(1)x^2+(-5)x+(-37)

Determine the a,b, and c
a=1
b=-5
c=-37

Use the formula:
x=(-b+-sqrt(b^2-4ac))/(2a)
x=(-(-5)+-sqrt((-5)^2-4(1)(-37)))/(2(1))
x=(5+-sqrt(25+37))/2
x=(5+-sqrt(62))/2

x_1=(5+sqrt(62))/2~~6.437
x_2=(5-sqrt(62))/2~~-1.437

In this case, the roots are real, their imaginary parts are 0
x_1~~6.437+0i
x_2~~-1.437+0i