分配律：乘法心算的基本原則(兩位數平方心算)

兩位數平方心算

1. $13^2=(13+3)\times(13-3)+3^2=16\times10+9=160+9=169$

2. $41^2=(41+1) \times (41-1)+1^2=42\times40+1=1680+1=1681$

3. $77^2=(77+3) \times (77-3)+3^2=80\times74+9=5920+9=5929$

4. $56^2=(56+4) \times (56-4)+4^2=60\times52+16=3120+16=3136$

5. $85^2=(85+5) \times (85-5)+5^2=90\times80+25=7200+25=7225$

6. $35^2=(35+5) \times (35-5)+5^2=40\times30+25=1200+25=1225$

7. $96^2=(96+4) \times (96-4)+4^2=100\times92+16=9200+16=9216$

練習

1. $14^2=$
2. $27^2=$
3. $65^2=$
4. $89^2=$
5. $98^2=$
6. $31^2=$
7. $41^2=$
8. $59^2=$
9. $26^2=$
10. $53^2=$
11. $21^2=$
12. $64^2=$
13. $42^2=$
14. $55^2=$
15. $75^2=$
16. $45^2=$
17. $84^2=$
18. $67^2=$
19. $103^2=$
20. $208^2=$

參考文章
Arthur Benjamin, Michael Shermer，《數學速算魔法》，稻田，新北市，民100.08。p.65~70