Question

calculeaza suma primilor trei termeni ai unei progresii aritmetice (an)n>1 stiind ca a2=4

Answer 1

$a_1+a_2+a_3=a_2-r+a_2+a_2+r=3a_2=3\cdot 4=12$

Answer 2

a1+a3=2a2
deci a1+a2+a3=3a2=3*4=12