The left and right focal points of the ellipse x2a2 + y2b2 = 1 (a > b > 0) are F1 and F2 respectively. The intersection of the straight line with an inclination angle of 120 ° through F2 and the ellipse is m. if MF1 is perpendicular to the X axis, the eccentricity of the ellipse is () A. 12−2311B. 2-3C. 2（2-3）D. 33

As shown in the figure, in RT △ mf1f2, ∠ mf2f1 = 60 °, F1F2 = 2C  MF2 = 4C, MF1 = 23cmf1 + MF2 = 4C + 23C = 2A {e = CA = 2-3, so B

If the two focuses of the ellipse x ^ 2 / 25 + y ^ 2 / 9 = 1 are F1 and F2 respectively, and the point P is any point on the ellipse, the perimeter of the triangle f1pf2 is calculated

a=5,b=3,c=4.
PF1+PF2=2a=10,F1F2=2c=8.
The perimeter of triangle f1pf2 = Pf1 + PF2 + F1F2 = 18

RELATED INFORMATIONS

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