The formula to calculate the ellipse foci is:
\[ f = \sqrt{a^2 - b^2} \]
Where:
An ellipse foci is defined as the locus of points in which the sum of the distance to each focus point is constant. To calculate an ellipse foci, square the distance from the center to the vertex and square the distance from the center to the co-vertex, subtract the latter from the former, then take the square root of the result.
Let's assume the following values:
Step 1: Square the distances:
\[ a^2 = 5^2 = 25 \]
\[ b^2 = 3^2 = 9 \]
Step 2: Subtract \( b^2 \) from \( a^2 \):
\[ 25 - 9 = 16 \]
Step 3: Take the square root of the result:
\[ f = \sqrt{16} = 4 \]
Therefore, the foci is 4.