If the sequence {an} satisfies A2 + A4 = 20, A3 + A5 = 40, then the common ratio q = () A. 12B. -12C. 2D. -2

If the sequence {an} satisfies A2 + A4 = 20, A3 + A5 = 40, then the common ratio q = () A. 12B. -12C. 2D. -2

∵ the sequence {an} satisfies A2 + A4 = 20, A3 + A5 = 40, ∵ A3 + A5 = q (A2 + A4) = 20q = 40, and the solution is q = 2

If S5 = 3 / 16, A3 = 1 / 4, then 1 / A1 1 / A2 1 / A3 1 / A4 1 / A5 =?

Let the common ratio be Q
s5=a1*(1+q+q²+q³+q&sup4)
a3=a1*q²
s5/a3=(1+q+q²+q³+q&sup4)/q²
=1+q+q²+1/q+1/q²
=3/4
q=-1/2

In AP {an}, D ≠ 0, A1, A3 and A9 are in equal proportion, and a1 + a3 + A9 / A2 + A4 + A10 is obtained

A3 = a1 + 2da9 = a1 + 8da3 / A1 = A9 / A3 (a1 + 2D) / A1 = (a1 + 8D) (a1 + 2D) 4D ^ 2-4a1d = 0d (d-a1) = 0 because D ≠ 0, d-4a1 = 0d = a1a3 = 3A1, A2 = 2A1, A4 = 4A1, A9 = 9a1, A10 = 10a1a1 + a3 + A9 / A2 + A4 + A10 = (1 + 3 + 9) A1 / (2 + 4 + 10) A1 = 13 / 16

In the same plane, there are A1, A2, A3. A10, 10 straight lines, if A1 ⊥ A2, A2 ∥ A3, A3 ⊥ A4 A9 ‖ A10, then the positions of A1 and A10
The relationship is ()
A vertical B parallel C may be vertical or parallel D uncertain

Choose B
It can be seen from the condition that the single serial number line is also vertical to the double serial number line (except A10), that is, the single serial number lines are parallel to each other, A9 ‖ a10