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5+9+13+...+101 suma gouse​

Răspuns :

5+9+13+...+101 =

= (4•1+1)+(4•2+1)+(4•3+1)+...+(4•25+1)

= 4•(1+2+3+...+25) + 1+1+1+...+1

= 4•[(25•(25+1)]/2 + 1•25

= 2•25•26 + 25

= 25•(2•26+1)

= 25•53

= 1325

5 + 9 + 13 + .. + 101 =

= (4×1 + 1) + (4×2 + 1) + ... + (4×25 + 1)

= 1×25 + 4(1 + 2 + .. + 25)

= 25 + 4×25×26 : 2

= 25 + 1300

= 1325