9: The normal vector is for instance n = (1,0). The tangent line is given by

n₁(x − x₀) + n₂(y − y₀) = 0.

Normal line is done similarly using the tangent vector.

If you want to go the "slope" way, the tangent slope is infinity, which means that the tangent line is vertical. This actually follows from the tangent vector. Consequently, the normal line is horizontal.

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