Question

if y is directly proportional to x when x = 6 and y = 12, write an equation to model the given relationship. Find the value of y if x = -30?

Answer 1

Since we have that y is directly proportional to x, then the relationship can be written like this:

$y=kx$

Now, since y=12 when x=6, we have the following:

$\begin{gathered} 12=k(6) \\ \Rightarrow k=\frac{12}{6}=2 \\ k=2 \end{gathered}$

Therefore, the equation would be y = 2x.

Finally, if x=-30, then:

$y=2(-30)=-60$