# Math Help - equation

1. ## equation

this is an equation... (x^2)/3 + (y^2)/5 = 15. this is an ellipse but how to calculate semi major axis from it?

2. Write the equation of ellipse in the standard form.

$\frac{x^2}{45} + \frac{y^2}{75} = 1$

Now can you find the semi-major axis?

3. ## check

it comes out to be (5*3^(1/2))/2. am i right?

4. Yes. You are right.

5. Originally Posted by vyomictor
it comes out to be (5*3^(1/2))/2. am i right?
No, you are not right. The semi-major axis is $\sqrt{75} = 5 \sqrt{3}$.

If you have the ellipse $\displaystyle \frac{x^2}{a^2} + \frac{y^2}{b^2}$ then the semi-major axis is either a (if a > b) or b (if b > a).