Prove that the algebraic expressions are equivalent. 
$$\frac{3^{k+1}-1}{2} + 3^{k+1} = \frac{3^{k+2}-1}{2}$$

with steps make left hand side = right hand side by modifying one or both expressions
Thanks for your help guys, I solved it like this:

$$\frac{3^{k+1}-1}{2} + 3^{k+1} = \frac{3^{k+1}-1}{2} + \frac{2*3^{k+1}}{2} = \frac{3^{k+2}-1}{2} $$


hint: $3^{k+1} = \dfrac{2\cdot 3^{k+1}}{2}$
