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zeion
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Homework Statement
The equation 5x^2 - 6xy + 5y^2 = 16 represents an ellipse.
Determine two points on the ellipse at which the tangent is horizontal.
Homework Equations
The Attempt at a Solution
I find the derivative of the equation:
(-10x + 6y) / (-6x + 10y) = 0 iff -10x + 6y = 0, so x = (3/5)y.
Then I sub x back into original equation and get y, I get y = +/- 1/(sqrt(2)), which is wrong.
What did I do wrong?