Question

Se considera numerele a=2+4+6+...+80 si b=1+3+5+...+79.Calculeaza a-b si a+b


Va rog mult

Answer 1

a=2+4+6+...+80
a =2×(1+2+3+...+40)
a = 2 × 40 × 41 : 2
a = 40 × 41
a = 1 640

b=1+3+5+...+79
aflam cati termeni are suma
(79 - 1) : 2 + 1 = 78:2+1 = 40
b = (1+79) × 40 : 2
b = 80 × 20
b = 1 600

a + b = 1 640 + 1600 = 3 240
a - b = 1 640 - 1 600 = 40