solve by factor , the positive square root of 21904
21904= 2 x 10952= 2 x 2 x 5476= 2 x 2 x 2 x 2738= 2 x 2 x 2 x 2 x 1369= 2 x 2 x 2 x 2 x 37 x 37= (2 x 2 x 37) x (2 x 2 x 37)= 148 x 148
