Question

Aratati ca:a)1 supra 2 x(2 grade+4 grade+6 grade+. +22 grade)=55 de grade.

Answer 1

Explicație pas cu pas:

$\frac{1}{2} \times (2 + 4 + 6 + ... + 22) = \frac{1}{2} \times 2(1 + 2 + 3 + ... + 11) \\ = \frac{11 \times 12}{2} = 60$

$\frac{1}{2} \times (2 + 4 + 6 + ... + 20) = \frac{1}{2} \times 2(1 + 2 + 3 + ... + 10) \\ = \frac{10 \times 11}{2} = 55$