Assertion (A): $a,b,c,d$ are position vectors of 4 points such that $2a-3b+7c-6d=0\Rightarrow a,b,c,d$ are coplanar. Reason (R): Vector equation of plane through three points $a,b,c$ is $\vec{r}=(1-x-y)a+xb+yc$.
Which is true?