Question

c)1+2+3+4+....+×=55​

Answer 1

Răspuns:

Explicație pas cu pas:

Aplicam Suma Gauss:

x(x+1)/2=55              x²+x=110           x²+x-110=0

x1,2=-1±√1+440/2=-1±21/2

x1=(-1+21)/2=20/2=10

x2=-1-21/2=-11  nu convine          x ∈N  

Raspuns:  x=10

Answer 2

$x \times (x + 1) \div 2 = 55 \\ x {}^{2} + x = 110 \\ x {}^{2} + x - 110 = 0 \\ (x - 10) \times (x + 11) = 0 \\ x = 10$

Verificare :

1+2+3+4+5+6+7+8+9+10=10(10+1)/2=5×11==》55