how did they get the line in red? (1 Viewer)

[bos1234]

 

[LoneShadow]

LOL:

let m = 3^k

then the line before the red line is = 0.5*(m-1+2m) = 0.5*(3m-1) <---the red line = 0.5*(3.3^k-1) = 0.5*(3^(k+1) -)

 

[pLuvia]

Basically it's just adding 'like terms'

Just imagine 1/2(3^k-1+2.3^k) equals to 1/2(1.3^k-1+2.3^k) and basically just addition from there

 

[kony]

the dot means multiplication, not decimal.