[أحمد سعد الدين]

area of ellipse

suppose semimajor axis of ellipse = a , and semiminor axis = b


The parametric formula of ellipse :

y = b*sin j
x = a*cos j

area of one - quarter of ellipse = INT (0 to a ) y.dx

dx = - a*sin j dj
when x = 0 ..... j = pi/2
when x = a ..... j = 0

area = 4*INT (from j = pi/2 to j = 0) - b*a*sin^2 j .dj

area = 4*INT (from j = 0 to j = pi/2)* a*b (1 - cos 2j)/2 . dj

area = 2*a*b [j - 1/2*sin 2j]from j = 0 to j = pi/2

area = 2*a*b [pi/2 - 0 - 1/2*sin pi + 1/2*sin 0

area = pi*a*b
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