Question

计算下列各式:15*15=___; 26*24

Answer 1

15*15=225(例外)

(a+b)(a-b)=a*a - b*b

26*24=(25+1)*(25-1)=25*25-1=624

37*33=(35+2)*(35-2)=35*35-4=1225-4=1221

71*79=(75+4)*(75-4)=75*75-16=5625-16=5609;