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how are you?i need one help and please give me some hint to solve it,namely we should construct equation of such ellipse,focuses of which are on the axis of abscisa and are symmetrical to origin,if distance between focus is equal to $4$ and semi-major axis is equal to $5$,generally we know that equation of ellipse is like

$$\left(\frac xa\right)^2 + \left(\frac yb\right)^2 = 1$$ where $a$ and $b$ are major and minor axes,but i dont know how to continue,so please help me.

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If $c$ is the distance from a foci to the origin, then $c^2=|a^2-b^2|$. You're given the values of $c$ and $a$. –  David Mitra Jan 20 '13 at 16:47
but distance between foci is same as distance between foci and center? –  dato datuashvili Jan 20 '13 at 16:51
The distance between the foci is $2c$ (your ellipse has center $(0,0)$, the foci are at $(-c,0)$ and $(c,0)$). –  David Mitra Jan 20 '13 at 16:54
thank you very much,i was confused about it –  dato datuashvili Jan 20 '13 at 16:57
So, dato, if you can solve it now, you can post your solution as an answer. Then, later, you can accept it. –  Gerry Myerson Jan 21 '13 at 0:52

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