Помогите пожалуйста !!! геометрические прогрессии # 1,2,3,4 #5 арифмечитеская

1)b1=1/8, b3=1/2
   b3=b1.qˇ2, qˇ2 = b3/b1=1/2 :1/8=1/2.8=4,q=V4=2.q=2
   s5=b1.(qˇ5-1)/q-1
  s5=1/8.(2ˇ5-1)/(2-1)=1/8.(32-1)/1=1/8.31=31/8
2)b5=1,b8=8
   b8=b5.qˇ3, qˇ3=b8:b5=8:1=8.q=2
   b5=b1.qˇ4,b1=b5/qˇ4,b1=1/16
s4=b1.(qˇ4-1)/(2-1)=1/16.(16-1)/1=1/16.15=15/16
3)b1=486,q=1/3,
  s4=486.(1/81 -1)/(1/3-1)=486.(-80/81)/(-2/3)=
= 6.80/2/3=480.3/2=720
4)b2=25/4,b3=5/4
   q=b3/b2=(5/4)/(25/4)=5/4. 4/25=20/100=1/5
  b4=b3.q=5/4.1/5=5/20=1/4
5)a2=7,a3=11
   d=a3-a2=11-7=4
   a1=a2-d=7-4=3, a10=a1+9.d=3+9.4=3+36=39
s10=10/2(a1+a10)=5.(3+39)=5.42=210
s10=210