[讨论]问个问题，各位大侠

u take a bunch of x, y values and plot a graph

y=mx+c, where u know c is definitely positive

therefore u know the y-intercept is going to be positive

so what's wrong if u got a graph that has a negative y-intercept?
    

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say we have applied force - friction = ma

F=ma+f

m is the slope, we measure diff F's and a's to plot the graph