Why this diagram is correct of cosine wave of the function which takes an argument as multiple of $2\pi$?

Question

Why the above diagram of $y(t)=\cos(2 \pi t)+1 ~$ adequate? since I thought as $t=1~$,

$y(1)=\cos\left(2 \pi \cdot \left(1\right)\right)+1=1+1=2~$ must be held however the actual diagram shows different result.

Is the diagram correct?

I assume that radian and degrees things are related to the problem.

What have I been missing?

Answer 1

The diagram is wrong; it actually shows the graph of $\cos\frac\pi2t+1$. Such mistakes with scaling graphs (e.g. does multiplying the argument by $2$ stretch or shrink the graph?) are unfortunately quite common.