Engineering
Mathematics
Standard Ellipse
Question

If cosα=  23 , then the range of values of φ for which the point whose eccentric angle φ on the ellipse x2 + 4y2 = 4 falls inside the circle x2 + y2 + 4x + 3 = 0 is

(π – α, π)

(α, π)

(– α, α)

(0, α)

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Solution

Let point (2cos φ, sin φ)

4cos2 φ + sin2 φ + 8cos φ + 3 = 0

3cos2 φ + 8cos φ + 4 < 0

(cos φ + 2) (3cos φ + 2) < 0

cosϕ<−23

cos φ < cos (π – α)

φ > π – α.