Question

What is the equation of this line?

Answer 1

We know the slope is 2 (because it increases 2 units every one unit) and the y-intercept is 0
y = mx + b
where m is the slope and b is the y intercept

y = 2x

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Answer 2

we know that

The equation of the line in the graph passes through the point $(0,0)$

so

the linear equation represent a direct variation  

A relationship between two variables, x, and y, represent a direct variation if it can be expressed in the form $y/x=k$ or $y=kx$

the constant of proportionality k is equal to the slope

We need only one point to determine the equation of the line

Let

$A(1,2)$

so

$(x,y)=(1,2)$

Divide the y-coordinate by the x-coordinate to find the slope

$m=\frac{y}{x}$

$m=\frac{2}{1}=2$

the equation is

$y=2x$

therefore

the answer is

the equation of the line is

$y=2x$