Question

How do you solve the equation by graphing `3x^2 + 9x = 12`?

Answer 1

You could graph the function and intersect it with a horizontal line at `y=12`

Explanation:

On your GC you would use `Y_1=3x^2+9x` and `Y_2=12`
And then the intersect -function. Make sure you set the windows at the right values. This usually takes some trying.

Easier:
At first we can divide everything by `3`
`->x^2+3x=4`
Then subtract `4` on both sides:
`->x^2+3x-4=0`
You can factor this into:
`->(x-1)(x+4)=0`
So:
`->x-1=0->x=1`
`orx+4=0->x=-4`