10^2+12^2+14^2+......+26^2=??
1 answer:
Answer:
3156
Step-by-step explanation:
- <em>Used formula:</em>
- <em>(1² + 2² + 3² + ... + n²) =1/6*n(n + 1)(2n + 1)</em>
--------
- 10²+12²+14²+......+26² =
- (2*5)²+(2*6)² + (2*7)² + ... + (2*13)² =
- 4*(5²+6²+7²+...+13²) =
- 4*(1²+2²+...+13² - (1²+2²+3²+4²)) =
- 4*(1/6*13(13+1)(2*13+1) - (1+4+9+16)) =
- 4*(1/6*13*14*27- 30) =
- 4*(819 - 30) =
- 4*789 =
- 3156
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