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**Phire** Hi, I want to get a solid understanding of the actual definition of a tangent line. I believe a tangent line is a line which touches the graph of another equation at one point? But is it always perpendicular to something at that point? I mean, if two perpendicular linear equations intersect with each other at 1 point, does that mean the lines are tangent to each other? I know that when finding tangent lines to circles, the line is always perpendicular to the radius, right? Is it possible to find a tangent line to a point on an equation like y=x^2 without using calculus?