Solution

ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2019/paper-2/11/a/ii/solution

The position vectors end at the midpoints of , and , respectively. The drawing places , and on those edges and shows the arrows from the origin. The volume of their parallelepiped is the absolute scalar triple product:
Equivalently, this is the absolute determinant of the matrix whose columns are the three vectors. Since it is nonzero, the vectors are linearly independent. Three linearly independent vectors in the three-dimensional vector space form a basis.

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