It's correct, but just with some typos. It should be $6(k+1)^2$ instead of $6+(k+1)$ on your third last line, and you missed a right bracket on your last line of proof. Also, usually it's easier to edit and look for us if you can type it in mathjax.
It's correct, but just with some typos. It should be $6(k+1)^2$ instead of $6+(k+1)$ on your third last line, and you missed a right bracket on your last line of proof. Also, usually it's easier to edit and look for us if you can type it in mathjax.