x 3 + y 3 = 1 7 2 9 x y .
Find the area of the figure bounded by the curveIf the answer comes as B A 2 where A and B are co-prime positive integers. Find A + B .
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I like your solution very much! I got a way of deriving the parametrization that you used before, by converting the equation x 3 + y 3 = 3 a x y into polar coordinates first, so we get r = cos 3 θ + sin 3 θ 3 a sin θ cos θ . for 0 ≤ θ ≤ 2 π . Then using the equations x = r cos θ , y = r sin θ , we obtain x = cos 3 θ + sin 3 θ 3 a sin θ cos 2 θ and y = cos 3 θ + sin 3 θ 3 a sin 2 θ cos θ Then dividing in each fraction the denominator and numerator by cos 3 θ . Then we get x = 1 + tan 3 θ 3 a tan θ and y = 1 + tan 3 θ 3 a tan 2 θ Now you can get the parametrization by making t = tan θ , and of course when 0 ≤ θ < 2 π , we have 0 ≤ t < ∞ . Is there any other way of deriving it?
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This is a very lucid and elegant explanation, as one would expect from a Cuban- and Soviet-trained mathematician. Thank you!
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Otto, I really appreciate you compliment, but, believe me, I am nothing compared to you. I am always learning from your solutions, and I am being sincere: you are a great professor and mathematician.
@Otto Bretscher sir... Well I didn't do this problem complete but I sought it(I am lazy at calculations sorry!!) As we know that the curve is symmetric about line y=x we can apply transformation on y=(X+Y)/√2 and x=(X-Y)/√2 which gave us an explicit function of Y in terms of X and 2 times the upper bound branch with the new horizontal axis would give the answer.
EDIT-the integral is solvable,it needs calculations and now I got the answer 1735.
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Yes, you can do it this way, but the computations are quite tedious.
What r u studying now and when we ll get all these in maths
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I had done a normal jee prep and started using the concepts...mathematics is the subject which I love the most
Nice sir!!! We've got similar solutions.. This is a very nice problem.
We can also solve this problem by converting the equation x 3 + y 3 = 3 a x y into polar coordinates. So we get r = cos 3 θ + sin 3 θ 3 a sin θ cos θ . Dividing both the numerator and denominator by cos 3 θ we obtain that r = 1 + tan 3 θ 3 a sec θ tan θ . Now the given area can be expressed as A = 2 1 ∫ 0 π / 2 r 2 d θ = 2 1 ∫ 0 π / 2 ( 1 + tan 3 θ ) 2 9 a 2 sec 2 θ tan 2 θ d θ = 6 9 a 2 ∫ 0 π / 2 ( 1 + tan 3 θ ) 2 d tan 3 θ = − 2 3 a 2 1 + tan 3 θ 1 ∣ ∣ ∣ ∣ 0 π / 2 = 2 3 a 2 . In this case a = 3 1 7 2 9 , so the area A = 6 1 7 2 9 2 , and, therefore, the answer is 1 7 3 5 .
You can also get the solution by usage of the formula for the cubic equation in y. This brings y 1 ( x ) , y 2 ( x ) , i.e. the two curves including the area wanted. After determination of maximum x to 914.872 by setting y 1 ( x ) = y 2 ( x ) you have the integration range to numerically calculate the integral of the area v between the two curves delivering v = 498240.1666 => 6 v = 1 7 2 9 2 .
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This is a Folium of Descartes , x 3 + y 3 = 3 a x y , with a = 3 1 7 2 9 . The loop C of this curve (i.e., the part in the first quadrant) can be parametrized by x = 1 + t 3 3 a t , y = 1 + t 3 3 a t 2 for t ≥ 0 . Thus the area enclosed by C is ∫ C x d y = − 9 a 2 ∫ 0 ∞ ( 1 + t 3 ) 3 t 2 ( t 3 − 2 ) d t = − 9 a 2 [ 6 ( 1 + t 3 ) 2 1 − 2 t 3 ] 0 ∞ = 2 3 a 2 = 6 1 7 2 9 2
The sum we seek is 1 7 3 5