Question

Fie o progresie geometrica cu b3=8 si q(ratia) =2
Aflati : b1,b9 si Suma.

Answer 1

Stim ca e prog.geometrica, stim pe b3 si q.
b3=b1*q²=> b1= b3/q²<=> b1= 8/4=2
Deci b1 este 2
b9=b1*q^8
b9=2*2^8=> b9= 2* 256= 512

Answer 2

[tex]b_1=b_3\cdot q^{-2} =8\cdot2^{-2} =8\cdot\dfrac{1}{4} =2 \\\;\\ b_9=b_1\cdot q^8=2\cdot2^8=2^9=512[/tex]