Question

Доведіть тотожність: (х - у)² + 2ху = х² + у².​

Answer 1

$\displaystyle\bf\\(x-y)^{2} +2xy=x^{2} + y^{2} \\\\x^{2} -2xy+y^{2} +2xy=x^{2} + y^{2} \\\\x^{2} +\underbrace{(2xy-2xy)}_{0}+y^{2} =x^{2} +y^{2} \\\\x^{2} +y^{2} =x^{2} +y^{2}$