Find the area of the ellipse: 3 x 2 + 4 x y + 3 y 2 = 1 [take π = 7 2 2 ]
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It can be easily observed that the ellipse is symmetrical about x=y & x=-y .Rest is a piece of cake.
A r e a o f a c o n i c s h a v i n g i t s c e n t e r a t o r i g i n i s o f t h e f o r m a x 2 + 2 h x y + b y 2 = 1 . h 2 − a b = 4 − 9 < 0 , w e c o n f i r m t h a t i t i s a n e l l i p s e . A n d s o , i t s a r e a = 4 a b − ( 2 h ) 2 2 π = 4 a b − ( 2 h ) 2 7 2 ∗ 2 2 = 7 ∗ 3 6 − 1 6 4 4 = 7 ∗ 2 ∗ 5 4 4 = 7 ∗ 5 2 2 .
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If the centre of any conic is at the origin then the coefficient of x and y will be zero in its general equation .
Any point on ellipse is ( r cos θ , r sin θ )
After satisfying these coordinates in the given equation and on simplifying we get,
3 r 2 + 2 r 2 sin 2 θ = 1
r = 3 + sin 2 θ 1 a = length of semi major axis b = length of semi minor axis
a = r m a x = 3 − 2 1 [ when denominator is minimum, r wil be maximum and minimum of sin 2 θ = − 1
b = r m i n = 3 + 2 1 { maximum of sin 2 θ = 1 ]
Area of ellipse = π a b
= 5 π
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