$a){91}^2={\left(90+1\right)}^2={90}^2+2\cdot 90\cdot 1+1^2=$  

$=8100+180+1=8281$  

$b){102}^2={\left(100+2\right)}^2={100}^2+2\cdot 100\cdot 2+2^2=$  

$=10000+400+4=10404$  

$c){203}^2={\left(200+3\right)}^2={200}^2+2\cdot 200\cdot 3+3^2=$  

$=40000+1200+9=41209$  

$d){39}^2={\left(40-1\right)}^2={40}^2-2\cdot 40\cdot 1+1^2=$  

$=1600-80+1=1521$  

$e){99}^2={\left(100-1\right)}^2={100}^2-2\cdot 100\cdot 1+1^2=$  

$=10000-200+1=9801$  

$f){498}^2={\left(500-2\right)}^2={500}^2-2\cdot 500\cdot 2+2^2=$  

$=250000-2000+4=248004$  

$g){33}^2-{31}^2=\left(33-31\right)\cdot \left(33+31\right)=2\cdot 64=128$  

$h){103}^2-{97}^2=\left(103-97\right)\cdot \left(103+97\right)=$   $6\cdot 200=1200$