If P=(x,y),F1=(3,0),F2=(−3,0) and 16x2+25y2=400, then PF1+PF2 equals
10
Given, 16x2+25y2=400 is the equation of ellipse.
⇒x225+y216=1
Here, a2=25,b2=16
We know, that in an ellipse distance of any point from its foci is constant and equal to length of the major axis, i.e.
PF1+PF2 = 2a
Now, PF1+PF2 = Major axis = 2a
=2×5=10