①縮小前，長：?$2.8\ \mathrm {cm}，$?寬：?$1.6\ \mathrm {cm}$?
?$ 2.8÷2×(1.6÷2)=1.12(\mathrm {cm}^2)$?
②縮小前，直徑為?$1.4\ \mathrm {cm}$?
?$ 3.14×(3×1.4÷2)^2=13.8474(\mathrm {cm}^2)$?
③放大前，底為?$1.7\ \mathrm {cm}，$?對應(yīng)的高為?$1.4\ \mathrm {cm}$?
?$ 2×1.7×1.4×2÷2=4.76(\mathrm {cm}^2)$?
④縮小前，邊長?$1.8\ \mathrm {cm}$?
?$1.8÷3×(1.8÷3)=0.36(\mathrm {cm}^2)$?
