First, we must know what the two variables in the equation y=mx+b really means.
The M represents slope while the B represents the Y-intercept.
With that out of the way, take a look at your top equation, y = 3/2x + ?. If you noticed the question mark is in the spot of the B (Y-intercept), we can simply find this by finding where on the graph does the line intercept the Y-axis.
Triangle B shows the Y-intercept to be -7, this means that the hypotenuse intercepts the Y-axis at (0 , -7).
If we were to find the (what I like to call) the interception point of triangle A's hypotenuse and the Y-axis, we find our missing variable.
Just looking at the graph, we can count and visually determine that the Y-intercept of the hypotenuse is (0 , 1).
Therefore, we can say: The equation of A's hypotenuse is: y = 3/2x + 1
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