Question

Gasiti primul termen a1  al progresiei aritmetice, daca:a) a31=301 si r=10 b)a41=-201 si r=-5 c)a51=0 si r=-2 d)a61=11,5 si r=0,5 ...va rog sa ma ajutati,,e urgent...macar la primul punct :((

Answer 1

an=a1+(n-1)*r=>a31=a1+30r=>301=a1+30*10=>301=a1+300=>a1=1 a41=a1+40r=>-201=a1+40*(-5)=>a1=-201+200=>a1=-1 a51=a1+50r=>0=a1+50*(-2)=>a1=100 a61=a1+60r=>11,5=a1+60*0,5=>a1=11,5-30=18,5