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### Course: Precalculus > Unit 5

Lesson 5: Foci of a hyperbola# Proof of the hyperbola foci formula

Sal proves why, for the general hyperbola equation x^2/a^2-y^2/b^2=1, the focal length f forms the equation f^2=a^2+b^2 with the parameters a and b. Created by Sal Khan.

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