In a correspondence diagram, which visual clue indicates that the underlying relation fails to be a function?

Which of these relations is NOT a function: $A=\left\{\right(1,2),(2,3),(1,4\left)\right\}$, $B=\left\{\right(0,1),(1,1),(2,1\left)\right\}$, $C=\left\{\right(3,4),(4,5),(5,6\left)\right\}$, $D=\left\{(7,8)\right\}$?

Given the continuous curve $y=\sin \left(x\right)$ restricted to domain $[-\frac{\pi }{2},\frac{\pi }{2}]$ and codomain $[-1,1]$, evaluate whether the restricted function has an inverse on the codomain, and if so, what is an explicit form for that inverse.

Evaluate $2^{-4}$.

An exponential function $f\left(x\right)=b^x$ passes through the points $(0,1)$, $(1,8)$, and $(2,64)$. What is the value of $b$?

Can the graph of a standard exponential function: $y=b^x$, where $b>0$ and $b\ne 1$, ever have an $x$-intercept?

Evaluate ${\log }_{49}\left(7\right)$.

Solve ${\log }_{{}_4}\left(x\right)=-3$ for $x$.

Find the inverse of $f\left(x\right)={10}^x+2$ in terms of $x$.

True or False: The statement ${\log }_{10}\left(1000\right)=3$ means ${10}^3=1000$.

Expand: ${\log }_{10}\left(20x^2{y}^3\right)$

Condense into a single logarithm: $4{\log }_5\left(x\right)-{\log }_5(x+2)$