 Solution

ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2023/paper-2/9/b/solution

In three dimensions each contracted Kronecker delta has value three, while

b_{k} b_{k} = ∣ b ∣^{2}

. Thus

δ_{jj} b_{k} b_{k} + δ_{ii} = 3∣ b ∣^{2} + 3 .

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