Question

I don't get it.... Can this be explained?

http://prntscr.com/aim100

−256
−84
84
86

Answer 1

@agent0smith

Answer 2

this mean sum of this 2*(-2)^(n-1)
for n=1 ,... till 7

a_1 = 2*(-2)^(1-1) = ?
a_2 = 2*(-2)^(2-1) = ?
a_3 = ?
a_4 = ?
--
a_7 = 2*(-2)^(7-1) =?

sum of this exression will be = a_1 +a_2 + ... +a_7 = ?

Answer 3

@Agl202 that's geometric serie , u know that right

Answer 4

\[2\frac{1-(-2)^{7-1} }{ 1-(-2) }\] @Agl202 this easy way for this sum

Answer 5

Wait! I'm trying to think here

Answer 6

\[S_{7}=42\] @Agl202

Answer 7

Oh I see what it adds up to. 86 r8t?

Answer 8

something miss in question @Agl202