Question

Aplicind formula ( a+b)(a-b) =a2-b2 calculaţi oral 101×99, 51 ×49 , 61× 59 , 102 ×98 , 32 × 28 , 43 × 37

Answer 1

101x99=(100+1)(100-1)=100^2-1^2=10000-1=9999
51x49=(50+1)(50-1)=50^2-1^2=2500-1=2499
61x59=(60+1)(60-1)=60^2-1^2=3600-1=3599
102x98=(100+2)(100-2)=100^2-2^2=10000-4=9996
32x28=(30+2)(30-2)=30^2-2^2=900-4=896
43x37=(40+3)(40-3)=40^2-3^2=1600-9=1591

Answer 2

101×99=9999
51×49=2499
61× 59=3599
102×98=9996
32×28=896
43×37=1591