Chapter 9 Quadratic Relations and Conic Sections - 9.4 Graph and Write Equations of Ellipses - 9.4 Exercises - Problem Solving - Page 639: 52d

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The standard form for an ellipse is: $\frac{x^2}{a^2}+\frac{y^2}{b^2}=1$ We know $a=300\\c=225$ Find $c^2=a^2-b^2\\\rightarrow b^2=a^2-c^2=(300)^2-(225)^2=39375$ Plug in values: $\frac{x^2}{90000}+\frac{y^2}{39375}=1$