# Math Help - Trig Problem

1. ## Trig Problem

Hey can you show me how to find the x- Intercepts for cos(y+Pi) = x^2 -x - 7

I tried a bunch of different things but I can't figure it out: the answer is supposed to be 3 (I like the faces )

2. Originally Posted by Mudd_101
Hey can you show me how to find the x- Intercepts for cos(y+Pi) = x^2 -x - 7

I tried a bunch of different things but I can't figure it out: the answer is supposed to be 3 (I like the faces )
as always, x-intercepts occur where y = 0. so plug in y = 0, we have

$\cos \pi = x^2 - x - 7$

$\Rightarrow -1 = x^2 - x - 7$

$\Rightarrow x^2 - x - 6 = 0$

just solve this quadratic equation for your intercepts (there are 2 answers)

3. Originally Posted by Mudd_101
Hey can you show me how to find the x- Intercepts for cos(y+Pi) = x^2 -x - 7

I tried a bunch of different things but I can't figure it out: the answer is supposed to be 3 (I like the faces )
It intercepts the x axis when y is zero!

$\cos(0+\pi) = x^2 -x - 7$

$\cos(\pi) = x^2 -x - 7$

$-1 = x^2 -x - 7$

$x^2 -x - 6 = 0$

$(x-3)(x+2) = 0$

$x = 3 \text{ or } x = -2$

4. OO thanks (silly me put x as 0)