I am confused with the inductive step of this very basic induction example in the book Discrete Mathematics and Its Applications:
$$1 + 2+· · ·+k = k(k + 1) / 2$$
When we apply $k+1$, the equation becomes:
$$1 + 2+· · ·+k+(k+1) = k+1(k + 1)+ 1 / 2 = (k+1)(k+2)/2$$
Now I am completely lost in the actual inductive step of the equation,
$$1 + 2+· · ·+k + (k + 1) = k(k + 1) 2 + (k + 1) = k(k + 1) + 2(k + 1) / 2 = (k + 1)(k + 2) / 2$$
As I understand it, we get
$$(k+1)(k+2)/2$$
when we substitute $k+1$ from $k$ in $k(k+1)/2$ and simplifying. How is $k(k + 1) / 2 + (k + 1)$ derived?
Can someone explain what this really means? I just simplified$ k+1(k + 1)+ 1 / 2 $to $(k+1)(k+2)/2 $it's in the book, but it suddenly becomes $k(k + 1) / 2 + (k + 1)$ and we just did the addition to turn it back to $(k+1)(k+2)/2$. How did it happen?
$\frac{k(k+1)}{2}$
for $\frac{k(k+1)}{2}$ or$\dfrac{k(k+1)}{2}$
for $\dfrac{k(k+1)}{2}$. $\endgroup$