Tính nhanh:

$$\begin{gathered} a) {73}^2-{27}^2; \\ b) {37}^2-{13}^2; \\ c) {2002}^2-2^2; \end{gathered}$$

Giải:

$$\begin{gathered} a) {73}^2-{27}^2 \\ =(73+27\left)\right(73-27) \\ =100.46 \\ =4600 \end{gathered}$$

$$\begin{gathered} b) {37}^2-{13}^2 \\ =(37+13\left)\right(37-13) \\ =50.25 \\ =100.12 \\ =1200 \end{gathered}$$

$$\begin{gathered} c) {2002}^2-2^2 \\ =(2002+2\left)\right(2002-2) \\ =2004.2000 \\ =400800 \end{gathered}$$