Question

b)1+2+3+4+...... +39 + 20 c) 5 + 10 + 15 + ... + 100 d) 121 . 13-121 - 1212 .​

Answer 1

Răspuns:

Explicație pas cu pas:

1+2+3+4+...... +39 + 20 = 39*40/2 + 20 = 39*20 + 20 = 20*(39 + 1)

= 20*40 = 800

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5 + 10 + 15 + ... + 100 = 5*(1 + 2 + 3 + ... + 20) = 5*20*21/2 = 5*10*21 = 1050

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121*13 - 121 - 1212 = 121*(13 - 1) - 1212 = 121*12 - 1212 = 1452 - 1212 = 240