Solution

ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2008/paper-1/17/a/ii/solution

The gradient is . At the three specified points it is respectively
Each vector is perpendicular to its straight boundary edge and points out of the triangle, where increases from its negative interior values. The arrows in the preceding figure mark these directions.

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