Parabola: tangency of line y = mx + c (Line y = mx + c touches y² = 4ax iff c = a/m)

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Line y = mx + c touches y² = 4ax iff c = a/m

What each symbol means

SymbolWhat it stands for
cIntercept
mSlope

When to use this

m ≠ 0; standard parabola y² = 4ax.