Given any real number c = 0 , the following system can be defined x 3 − 3 x y 2 + 3 c y 2 − 3 c x 2 + 4 c 2 x − 2 c 3 − y 3 + 3 x 2 y − 6 c x y + 4 c 2 y = 0 = 0 Find the exact number of solutions ( x , y ) , where x and y are real numbers and y = 0 .
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The equations: c = 0 y = 0 − 2 c 3 + 4 x c 2 − 3 x 2 c + 3 y 2 c + x 3 − 3 x y 2 = 0 − y 3 + 4 c 2 y + 3 x 2 y − 6 c x y = 0 ⟹ Over C Over R ⎣ ⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎡ x → c x → c x → ( 1 − 2 i ) c x → ( 1 − 2 i ) c x → ( 1 + 2 i ) c x → ( 1 + 2 i ) c y → − c y → c y → − 2 c y → 2 c y → − 2 c y → 2 c ⎦ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎤ [ x → c x → c y → − c 2 y → c 2 ]
In either case, there are 2 real solutions.
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The given system is equivalent to the polynomial equation z 3 − 3 c z 2 + 4 c 2 z − 2 c 3 = 0 , where z = x + i y . Since the equation has the solutions c , c + c i and c − c i , then the corresponding solutions of the system are the pairs ( c , 0 ) , ( c , c ) and ( c , − c ) , and, therefore, the answer is 2.