Question

Calculați:
$(2 \times 0 + 1) + (2 \times 1 + 1) + (2 \times \: 2 + 1) + ... + (2 \times 10 + 1)$
......
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Answer 1

2×0+1+2×1+1+2×2+1+...+2×1×+1=

2×0+2×1+2×2+2×3+...+2×10+1×11=

2(0+1+2+3+...+10)+11=

2(10×11÷2)+11=

2(110÷2)+11=

2×55+11=

110+11=121