1+2+3+.........+47+48+49=..... tolong isi cara supaaya saya mengerti!!

1 + 2 + 3 + ... + 49 =

U₁ = a = 1
  b = 2 - 1 = 1

Un = a + (n - 1) x b
 49 = 1 + (n - 1) x 1
 49 = 1 + n - 1
   n = 49

Sn = n/2 x (a + Un)
      = 49/2 x (1 + 49)
      = 49/2 x 50
      = 1.225

semoga jelas dan membantu ya

Geometri

[(49 - 1 + 1) × (49 + 1)] : 2 × 1
= (49 × 50) : 2 
= 2450 : 2
= 1225