Question

An equation where y varies directly as x and y = 28 when x = 7

Answer 1

If y varies directly as x, the equation is like

$y = kx$

To find the value of k, plug the known values:

$28 = 7k \iff k = \dfrac{28}{7} = 4$

Answer 2

Answer:

[tex] y=4x [tex/]

Step-by-step explanation:

Any linear or direct variation can be written as:

[tex] y=mx [tex/]

In this equation x represents the independent variable and y the dependent variable, so, y is always obtained evaluating the variable x. Furthermore, m is the only parameter to determine.

In this particular case we know both values of x and y. Remplacing it in the equation above we have:

[tex] 28 = k*7 [tex/]

Solving this equation we obtain:

[tex] m = 28/7 = 4 [tex/]

Therefore:

[tex] y = 4x [tex/]