square of a number: n^2=(n+1)^2-(n+1)-n square of a number =square of a after number-(after number)-(number) example=9^2=10^2-10-9 =100-10-9 =100-19 =81 19^2=20^2-20-19 =400-39 =361 29^2=30^2-30-29 =900-30-29 =841 39^2=40^2-40-39 =1600-40-39 =1521 49^2=50^2-50-49 =2500-50-49 =2401