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Activity 9.5.2

Avg difficulty 2.5

Suppose u⃗=⟨0,1,3⟩\vu = \langle 0, 1, 3\rangle and v⃗=⟨2,−1,0⟩\vv = \langle 2, -1, 0\rangle. Use equation this equation for the following.

  1. Find the cross product u⃗×v⃗\vu\times\vv.

  2. Evaluate the dot products u⃗⋅(u⃗×v⃗)\vu\cdot(\vu\times\vv) and v⃗⋅(u⃗×v⃗)\vv\cdot(\vu\times\vv). What does this tell you about the geometric relationship among u⃗\vu, v⃗\vv, and u⃗×v⃗\vu\times\vv?

  3. Find the cross product v⃗×ı^\vv\times \vi.

  4. Recall that multiplication of real numbers is associative. For example, (2⋅5)⋅3=2⋅(5⋅3)(2\cdot 5)\cdot 3 = 2\cdot(5\cdot 3). Is it true that the cross product of vectors is associative? For instance, is it true that (u⃗×v⃗)×ı^=u⃗×(v⃗×ı^)(\vu\times\vv)\times\vi = \vu\times(\vv\times\vi)?

  5. Find the cross product u⃗×u⃗\vu\times\vu and write a sentence or two to explain the meaning of your result.

Long, Keller & Schlicker, Active Calculus Multivariable, §9.5 The Cross Product, Activity 9.5.2

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Adapted from Active Calculus Multivariable © 2013–2026 Nicholas Long, Mitchel T. Keller, and Steven Schlicker. Licensed under CC BY-SA 4.0. Source: Active Calculus Multivariable. Imported at revision 692c03c.