1 2 − x 2 3 + 4 x 2 − x 2 3 = 4 x 2
Find the sum of all solutions x .
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Ok my solution 1 2 − x 2 3 + 4 x 2 − x 2 3 = 4 x 2 Let x 2 = a > 0 ⇒ 1 2 − a 3 + 4 a − a 3 = 4 a ⇔ 4 a − a 3 = 4 a − 1 2 − a 3 ⇒ 4 a − a 3 = 1 6 a 2 − 8 a 1 2 − a 3 + 1 2 − a 3 ⇔ 4 a 2 − 2 a 1 2 − a 3 − a + 3 = 0 ⇔ 4 a 2 − a − 4 8 a 2 − 1 2 a + 3 = 0 ⇔ 1 2 a ( 4 a − 1 ) − 1 2 1 2 a ( 4 a − 1 ) + 3 6 = 0 Let 1 2 a ( 4 a − 1 ) = y ≥ 0
⇒ y 2 − 1 2 y + 3 6 = 0 ⇒ y = 6 ⇒ 4 8 a 2 − 1 2 a = 3 6 ⇒ a = 1 a = − 4 3 Because of a > 0 So a = 1 ⇒ x = ± 1 S = 1 − 1 = 0
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In the given equation, if x is a solution, then so is − x . Therefore, S = 0 .