Explicație pas cu pas:
1) a1=-3
a2= a1+r=(-3)+(-2)=-5
a3=-5+(-2)=-7
S3=(-3)+(-5)+(-7)=-3-5-7=-15
2) b1=-3
b2=b(2-1)×q=b1×(-2)=(-3)×(-2)=6
b3=6×(-2)=-12
S3=b1(q la puterea n -1)/(q-1)=[(-3)×(-2)³-1]/(-2)-1=-3×[(-8)-1]/-3=-3×(-9)/-3=27/-3=-9
3) x=?
a1=2x-5
a2=3x
a3=-10
a2=(2x-5)+r=3x
2x-3x=5-r
-x=5-r|×(-1)
x=-5+r=r-5
a3=(r-5)+r=2r-5=-10
2r=-10+5
r= -5/2
a2=a3-r= -10-(-5/2)=-10+5/2=(-20+5)/2=-15/2
=>(2x-5)+(-5/2)=-15/2
2x=-15/2+5/2
2x=-10/2=-5
x=-5/2
