Question

How do you solve `5r^2 = 80` using the quadratic formula?

Answer 1

`+- 4`

Explanation:

`ax^2+bx+c=0`
`5r^2+0r+(-80)=0`

`x=(-b +- sqrt(b^2-4ac))/(2a)`
`r=(0+- sqrt(0^2-4*5*-80))/(2*5)`

`r=(0+- sqrt(0+1600))/10`
`r=+- 40/10`
`r=+- 4`

Answer 2

`r=+-4`

Explanation:

`"Alternative method to quadratic formula"`

`"divide both sides by 5"`

`rArrr^2=16`

`color(blue)"take the square root of both sides"`

`rArrr=+-sqrt16larrcolor(blue)"note plus or minus"`

`rArrr=+-4`