[cardinopolynomial]

ข้อความเดิมเขียนโดยคุณ banker

$2x^2 + 2y^2 = \frac{42}{x+y} + \frac{12}{x-y} $

$x^2 + y^2 = \frac{21}{x+y} + \frac{6}{x-y} $

$2xy = \frac{12}{x-y} - \frac{42}{x+y}$

$(x+y)^2 = \frac{21}{x+y} + \frac{6}{x-y} + \frac{12}{x-y} - \frac{42}{x+y}$

$(x+y)^2 = \frac{63}{x+y} - \frac{6}{x-y}$

ตรงนี้ครับ

$(x+y)^2 = \frac{-21}{x+y} + \frac{18}{x-y}$