Question

Which is the direct linear variation equation for the relationship?

y varies directly with x and y = 10 when x = 2.


A.
y = 2x + 6

B.
y = x + 8

C.
y = x – 8

D.
y = 5x
@greenlegodude57 @SolomonZelman ? Can you help?

Answer 1

When you see the words ` y varies directly with x ` that simply means \(\large\color{midnightblue}{ \rm y=kx }\) where k is a constant.
You are given that `y=10` and `x=2 ` So,
\(\large\color{midnightblue}{ \rm y=kx }\)
\(\large\color{midnightblue}{ \rm 10=k(2) }\)
\(\large\color{midnightblue}{ \rm 5=k }\) thus the equation would be
\(\large\color{midnightblue}{ \rm y=5x }\)

Answer 2

What I would do is, exclude all options besides D, because they have a y-intercept other than zero. That means NOT direct variation.

Answer 3

Oh, okay! Thank you!