Question

Va rog frumos cine imi face ex :
b)2+2la2+2la3+2la4+...+2la20=

c )2+2la2+2la3+2la4+...+2la200=


Urgent!Va rog!

Answer 1

Stim ca: $S_{n}=b_{1}\times \frac{ q^{n}-1 }{q-1}$

b)
$\\ b_{1}=2 \\ q=2 \\ n=20 \\ \\ S_{20} = 2\times \frac{ 2^{20}-1 }{2-1} \Rightarrow S_{20} = 2^{21}-2$

c)
$\\ b_{1}=2 \\ q=2 \\ n=200 \\ \\ S_{200} = 2\times \frac{ 2^{200}-1 }{2-1} \Rightarrow S_{200} = 2^{201}-2$