$a)8^2=8\cdot 8=64$

$b){12}^2=12\cdot 12=10\cdot 12+2\cdot 12=120+24=144$ $b){12}^2=12\cdot 12=10\cdot 12+2\cdot 12=120+24=144$

$c){41}^2=41\cdot 41=40\cdot 41+1\cdot 41=1640+41=1681$

$d){2,5}^2=2,5\cdot 2,5=2\cdot 2,5+0,5\cdot 2,5=5+1,25=6,25$

$e){\left(\frac{2}{3}\right)}^2=\frac{2}{3}\cdot \frac{2}{3}=\frac{4}{9}$