$a){\left(x+2\right)}^2=x^2$  

$x^2+4x+4=x^2\mid -x^2$  

$4x+4=0\mid -4$  

$4x=-4\mid :4$  

$x=-1$  

$b){\left(2-3x\right)}^2-{\left(1+2x\right)}^2-3x^2=2x^2$  

$4-12x+9x^2-\left(1+4x+4x^2\right)-3x^2=2x^2$  

$5x^2-16x+3-3x^2=2x^2$  

$2x^2-16x+3=2x^2\mid -2x^2$  

$-16x+3=0\mid -3$  

$-16x=-3\mid :\left(-16\right)$  

$x=\frac{3}{16}$  

$c){\left(x+2\right)}^2=x^2-2$  

$x^2+4x+4=x^2-2\mid -x^2$