Using the standard equation of an ellipse whose major axis is along the x axis, a=5 and b=3. what is the distance between the center to each foci?

With ellipse the equation to find c or the distance from the center to the foci is c^2 = a^2 - b^2.  So if you plug those numbers in you get:
c^2 = 25 - 9
c^2 = 16
c = 4
The distance from the center to each foci is 4

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