Take the tour ×  I was trying to figure out the step between
these two equal expression:  $$(2k)\cdot 2^{k+1} = k\cdot
2^{k+2}$$  share|improve this question Does the "." represent
multiplication? –  Edison Apr 29 '12 at 5:04 $(2k)\cdot
2^{k+1}=k(2\cdot 2^{k+1})=k(2^{(k+1)+1})=k\cdot 2^{k+2}$. – 
Brian M. Scott Apr 29 '12 at 5:05 @BrianM.Scott: that's it!! I
was thinking how the k goes out. It is the associative law!!
Thank you all. –  MIH1406 Apr 29 '12 at 5:09 add comment  1
Answer  up vote 1 down vote accepted  HINT A number raised to an
exponent tells you how many times to multiply that number by
itself.  For example: $2^{k}=2*2*...*2$ k-times, so
$2*2^{k}=2*(2*2*...*2)$ a total of $k+1$ times so
$2*2^{k}=2^{k+1}$  share|improve this answer add comment  Your
Answer