по математике. Ст 214. Номер524

A) 21 + 22 + 23 +..30
a₁ = 21
a₂ = 22
d = 22 - 21 = 1
Числе таких будет 10. Их сумма будет равна:
S₁₀ = (2*a₁ + d(n - 1)) / 2)) * n = (2*21 + 9)) / 2)) * 10 = (51/2) * 10 = 25,5*10 = 255
ответ: 255

б) 5 + 10 + 15 + 20... +100
a₁ = 5
a₂ = 10
d = 10 - 5 = 5
Числе таких будет 20. Сумма их будет равна:
S₂₀ = (2*a₁ + d(n - 1)) / 2)) * n = (2*5 + 5*19) / 2)) * 20 = (10 + 95) / 2)) * 20 = 52,5*20 = 1050
ответ: 1050

в) 93 + 83 +..+23 + 13 + 3
a₁ = 93
a₂ = 83
d = 83 - 93 = -10
Чисел таких будет 10. Сумма их будет равна:
S₁₀ = (2*a₁ + d(n - 1)) / 2)) * n = (2*93 - 10*9) / 2)) * 10 = (186 - 90) / 2)) * 10 = (96/2)*10 = 48*10 = 480
ответ: 480

142800:4 = 35700                               29004:6 = 4834
   _142800| 4                                              _ 29004| 6                                     
     12        | 3 5 7 0 0                                     24      | 4 8 3 4
     _22                                                           _50
       20                                                             48
         28                                                           _20
         28                                                             18
           0                                                               24
             0                                                             24
                                                                                                  
             0                                                               0
 
     509700:5 = 101940
           _509700| 5
             50        |1 0 1  9 4 0
               _9
                 0
               _9
                 5
               _47
                 45
                 _2
                   0
                
                   2