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S=150 + 160 + ... + 830 =


Răspuns :

S=150 + 160 + ... + 830

S = 10×(15+16+...+83)

S = 10 × [ ( 1+2+3+...+83) - (1+2+3+...+14)]

S = 10 × ( 83 × 84 : 2 - 14 × 15 : 2)

S = 10 × ( 83 × 42 - 7×15)

S = 10 × ( 3 486 - 105)

S = 10 × 3 381

S = 33 810