1)a1q-a1=-4⇒a1(q-1)=-4⇒a1=-4/(q-1))
a1q²-a1=8⇒a1(q²-1)=8⇒a1=8/(q²-1)
-4/(q-1)=8/(q-1)(q+1)
q+1=-2
q=-3
a1=-4/(-3-1)=1
1;--3;9;-27;...
2)a1+a1q³=0,4375⇒a1(1+q³)=0,4375
a1q²-a1q+a1=0,875⇒a1(q²-q+1)=0,875
a1(1+q)(1-q+q²)=0,4375
(1+q)*0,875=0,4375
1+q=0,4375:0,875
1+q=0,5
q=-0,5
a1=0,4375:(1-0,125)
a1=0,4375:0,875
a1=0,5
0,5;-0,25;0,125;...