Question

aratati ca d=2×(1+2+3+...+124)+125 este cub perfect

Answer 1

$d = 2 \times (1 + 2 + 3 + ... + 124) + 125$

$d = 2 \times \frac{124(124 + 1)}{2} + 125$

$d = 124(124 + 1) + 125$

$d = 124 \times 125 + 125$

$d = 125(124 + 1)$

$d = 125 \times 125$

$d =5\times 5\times 5\times 5 \times 5 \times 5$

$d=25 \times 25 \times 25={25}^{3}=>c.p$