\(\sqrt{2x^2+5x+2}\) -2\(\sqrt{x^2+5x-6}\)=1

cách 1: (a +b- c)² - (a-c)² -2ab + 2bc

= a² + b² +c² +2ab - 2bc - 2ac -a² + 2ac -c² -2ab +2bc

=b²

cách 2: (a + b -c )² - (a-c)² -2ab+ 2bc

=\(\left[\left(a+b-c\right)^2-\left(a-c\right)^2\right]\)-2ab +2bc

=(a+b-c+a-c)(a+b-c-a+c) -2ab +2bc

= (2a+b-2c)b -2ab+ 2bc

=2ab+b² -2bc -2ab +2bc

=b²