# Homework Help: Find zeros of quadratic equation

1. Jun 21, 2011

### Torshi

1. The problem statement, all variables and given/known data
Find the zeros of the quadratic equation?

2. Relevant equations

P(x)=4(x+7)^2+(x+7)-3

3. The attempt at a solution

I substituted and made it 4u^2+u-3 ?? Then after that I factor then back substitute?? I'm not sure how to back substitute tho.

2. Jun 22, 2011

### Arianwen

Think about what u is equal to when you make the substitution. If you have that and the value for u, finding x should be straightforward.

3. Jun 22, 2011

### gb7nash

What's the equation for u in terms of x? Once you have this, solve for x in the equation and plug in the values you got for u.

4. Jun 23, 2011

### Skins

You did a change of variables. You substituted u for x where u = x+7 to get the equation

$$f(u) \, = \, 4u^{2} \, + \, u \, - \, 3 \, = \, 0$$

solve for u in the above expression then use u = x + 7 to find x for each u.

i.e. since u = x+7 then x = u - 7 gives you x.