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Show that the equation for a plane through the points $(x_1,y_1,z_1),(x_2,y_2,z_2),(x_3,y_3,z_3)$ can be written as $$\begin{vmatrix}x&y&z&1\\x_1&y_1&z_1&1\\x_2&y_2&z_2&1\\x_3&y_3&z_3&1\end{vmatrix}=0$$

Is there some clever way of doing this that is not just brute force calculations of the determinant and then calculate the norm vector for the plane, which will be the coefficients for x,y,z-values in the plane equation: $$\begin{pmatrix}x_3-x_1\\y_3-y_1\\z_3-z_1\end{pmatrix}\times\begin{pmatrix}x_2-x_1\\y_2-y_1\\z_2-z_1\end{pmatrix}$$

and then calculate the equations constant by scalar multiply the norm vector with one of the points.

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$$\begin{vmatrix}x&y&z&1\\x_1&y_1&z_1&1\\x_2&y_2&z_2&1\\x_3&y_3&z_3&1\end{vmatrix}=0$$ implies that the four columns $C_1,C_2,C_3,C_4$ are linearly dependent. And therefore that it exists $a,b,c,d$ non all equal to zero such that $aC_1 + bC_2+cC_3+dC_4=0$, i.e. that

$$ax+by+cz+d=0$$ is an equation of a plane containing the three initial points $P_1,P_2,P_3$.

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  • $\begingroup$ Is this determinant equation a useful way to calculate the general equation for a plane through 3 points? $\endgroup$ Commented Nov 18, 2021 at 14:30
  • $\begingroup$ I think that using the cross product of $P_2-P_1, P_3-P_1$ is more efficient from a computation standpoint. $\endgroup$ Commented Nov 18, 2021 at 14:35
  • $\begingroup$ Thank you. I think my book want me to contemplate linear dependency, so that is what I will take form the problem. $\endgroup$ Commented Nov 18, 2021 at 14:37

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