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10-2. Parabola, Ellipse, Hyperbola
medium
If the line $y = 2x + c$ be a tangent to the ellipse $\frac{{{x^2}}}{8} + \frac{{{y^2}}}{4} = 1$, then $c = $
A
$ \pm 4$
B
$ \pm 6$
C
$ \pm 1$
D
$ \pm 8$
Solution
(b) $c = \pm \sqrt {{b^2} + {a^2}{m^2}} = \pm \sqrt {4 + 8.4} = \pm 6$.
Standard 11
Mathematics