Предмет: Математика, автор: alik5075

СРОЧНОООООООООООООО 4

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Ответы

Автор ответа: Hoang3000

Ответ:

Пошаговое объяснение:

200+400+...+800+1000=100*(2+4+6+8+10)=100*30=3000

7+14+21+...+91+98=7*(1+2+3+...+14)=7*(14*15/2)=7*7*15=49*15=735

101-97+93-89+...+5-1=(101-97)+(93-89)+...+(5-1)=4+4+...+4=13*4=52

всего 26 чисел, разобьем их на 13 пар

1+2+3+...+n

n+...+3+2+1

--------------------

(n+1)+(n+1)+...(n+1)=(n+1)*n=>1+2+3+...+n=(n+1)*n/2

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