31.5. Вычислите с формулы a ^ 2 - b ^ 2 = (a - b)(a + b)

1) (13-9)•(13+9)=4•22=88

2)(20-19)(20+19)=1•39=39

3)(2,2-2,8)•(2,2+2,8)=-0,6•5=3

4)(3,5-3,7)(3,5+3,7)=-0,2•7,2=-1,44

5)(5/6-2/3)(5/6+2/3)=1/6•9/6=1/4 или =0,25

6)(7/9-1/6)(7/9+1,6)=11/18•17/18=187/324

7)(5/12-3/4)(5/12+3/4)=-4/12•12/12=-1/3

8)(3/10-4/5)(3/10+4/5)=-5/10•11/10=-55/10=-11/2=-5,5

9)(8/15-4/5)(8/15+4/5)=-4/15•20/15=-80/225=-16/45

10)(15/7-15/7)(15/7+15/7)=0•30/7=0

11)(10/3-9/2)(10/3+9/2)=-7/6•47/6=-329/36=9⁵/³⁶

12)(31/6-22/3)

(31/6+22/3)=-13/6•75/6=-13/2•25/6=-325/12

13)(51-41)(51+41)=10•92=920

14)(54-46)(54+46)=10•100=1000

15)(76-24)(76+24)=52•100=5200

16)(328-172)(328+172)=156•500=78000

17)(11/3-7/3)(11/3+7/3)=4/3•18/3=8

18)(68/9-40/9)(68/9+40/9)=28/9•108/9=28•12/9=28•4/3=112/3