Using (x+a)(x+b)=x²+(a+b)x+ab, find (i) 103×104 (ii) 5.1×5.2 (iii) 103×98 (iv) 9.7×9.8

i) 103×104 = (100+3)(100+4) = (100)²+(3+4)100+(3)(4) = 10000+700+12 = 10712
ii) 5.1×5.2 = (5+0.1)(5+0.2) = (5)²+(0.1+0.2)5+(0.1)(0.2) = 25+1.5+0.02 = 26.52
iii) 103×98 = (100+3)(100-2) = (100)²+(3-2)100+(3)(-2) = 10000+100-6 = 10094
iv) 9.7×9.8 = (9+0.7)(9+0.8) = (9)²+(0.7+0.8)9+(0.7)(0.8) = 81+13.5+0.56 = 95.06