a^2-4b^2=(a-2b)(a+2b)=(13.2-2*3.2)(13.2+2*3.2)=6.8*19.6=133.28(平方厘米)
a^2-4b^2=(a+2b)(a-2b)=(13.2+6.4)(13.2-6.4)=19.6*6.8=133.28(cm^2)
a^2-4^b2=(a-2b)(a+2b)=6.8*19.6=133.28
