Solution: The tangent vector of curve s=( 1, -2t, 3t^2), and the normal vector of plane n=( 1, 2, 1).

S * n = 1-4t+3t 2 = 0, and the solution is: t= 1 or 1/3, because there are only two solutions, there are only two.

I wonder if the answer is right.

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