S₄=-80 S₃=-23 b₁=-2 q=?
S₄-S₃=(b₁+b₁q+b₁q²+b₁q³)-(b₁+b₁q+b₁q₂)=-80-(-26)
b₁+b₁q+b₁q²+b₁q³-b₁-b₁q-b₁q=-54
b₁q³=-54
(-2)*q³=-54 |÷(-2)
q³=27
q³=3³
q=3.
14x-8x²+42-24x=16x+2-8x²-x+15
14x-8x²-24x-16x+x+8x²=2+15-42
-25x=-25
x=25/25
x=1
Ответ : 1
4 3/10 - (-2 5/8) = 43/10 + 21/8 = 172/40 + 105/40 = 277/40 = 6,925