Question

Dovedeste ca n=1+2+3+...+20+75 : 5 e patrat perfect

Answer 1

$n = 1 + 2 + 3 + ... + 20 + 75 \div 5$

$n = \frac{20(20 + 1)}{2} + 15$

$n = \frac{20 \times 21}{2} + 15$

$n = 10 \times 21 + 15$

$n = 210 + 15$

$n = 225 = {15}^{2} = > n \: este \: p.p$

Answer 2

(20x21) : 2 + 15 =
= 420: 2 + 15=
=210 + 15=
=225=> 15 la puterea a doua, deci este patrat perfect