Odpowiedź:
1]
a6=a1+5r=4+5*(-4)= -16
a20=a1+19r=4+19*(-4)=-72
2]
a21=a5+16r 8=4+16r 16r=4 r=4/16=1/4
a5=a1+4r 4=a1+4*1/4 a1=3
an= 3+(n-1)*1/4= 1/4 n -1/4+3=1/4 n + 2 3/4
3]
aₙ₊₁-aₙ= 3(n+1)-1-(3n-1)= 3n+3-1-3n+1=3= const
aₙ₊₁-aₙ= [6- (n+1) ]/2 - (6-n)/2= (6-n-1-6+n)/2= -1/2 = const
4]
a1=3 a2=7 r=4 a9=a1+8r=3+8*4=35
S9=(a1+a9)/2 *9=(3+35) *4,5 = 171
a21=a1+20r= 3+20*4=83 S21= (a1+a21)/2 *21=(3+83) *10,5=903
5]
a1=4 a2=8 r=4 an= a1+(n-1)*r 112= 4+(n-1)*4
108=4n-4 4n= 112 n=28 wyrazów
a1=2 a12= a1+11r= 2+11*3=35
S12=(a1+a12)/2 *12=(2+35)*6=222
Szczegółowe wyjaśnienie:
