# Tangent zeros with a calculator?

1. Feb 26, 2015

### Tyrion101

I'm tasked with findings he solutions to a particular tangent equation, and when I did it before with sine it was just a matter of plugging in the equation to the calculator, then getting all the zeros. Since it is tangent now and not sine, do I do something special? Is it no longer the x value anymore?

2. Feb 26, 2015

### Staff: Mentor

This is too vague to answer. What is the equation?

Also, if this is a specific homework or textbook question, it should be posted in the Homework & Coursework section, not here in the technical math sections.

3. Feb 26, 2015

### Tyrion101

3tan^2x+4tanx-15, I do not want an answer but want to know as this is a standard quadratic what variable am I looking for when I punch in the zero program on my calculator. Or if I'm looking for the wrong thing entirely.

4. Feb 26, 2015

### SteamKing

Staff Emeritus
This appears to be a case where you are trying to let your calculator do your thinking for you.

If you are trying to solve the equation 3tan2 x + 4tan x - 15 = 0, then a substitution of u = tan x would seem appropriate first.

Once you find out for which values of u the equation is true, then you worry about finding the values of x.

5. Feb 26, 2015

### Tyrion101

It's a problem where it tells me to use the calculator. In fact it states it at the very beginning of the problem. I'm unfamiliar with the ti-89.

6. Feb 26, 2015

### SteamKing

Staff Emeritus
In order to find the values of u = tan x for which the equation is true, yes, I agree that a calculator will be necessary. But my point was that you are trying to apply the calculator before you have finished analyzing the equation, to put it into a form amenable for finding a solution with the calculator.

There are sites online where you can download a manual for the TI-89 and which can probably show you how to use its various functions to solve your equation.

7. Feb 26, 2015

### Staff: Mentor

I strongly agree. Think first, then use a calculator.