Question

Докажите тождество:(х+2у) ^2-(х-2у) ^2=8ху

Answer 1

(x+2y)^2-(x-2y)^2=8xy;

x^2+4xy+4y^2-(x^2-4xy+4y^2)=x^2+4xy+4y^2-x^2+4xy-4y^2=4xy+4xy=8xy.