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Exercise 13

Avg difficulty 2.5

This problem is a continuation of the previous problem.

  1. Let us define vectors v1=[52],   v2=[−11]\vvec_1 = \twovec{5}{2}, ~~~ \vvec_2 = \twovec{-1}{1}. Show that Av1=v1,   Av2=0.3v2A\vvec_1 = \vvec_1, ~~~A\vvec_2 = 0.3\vvec_2.

  2. Suppose that x1=c1v1+c2v2\xvec_1 = c_1 \vvec_1 + c_2 \vvec_2 where c1c_1 and c2c_2 are scalars. Use the Linearity Principle expressed in Linearity of matrix multiplication to explain why x2=Ax1=c1v1+0.3c2v2\xvec_{2} = A\xvec_1 = c_1\vvec_1 + 0.3c_2\vvec_2.

  3. Continuing in this way, explain why x3=Ax2=c1v1+0.32c2v2x4=Ax3=c1v1+0.33c2v2x5=Ax4=c1v1+0.34c2v2\begin{aligned} \xvec_{3} = A\xvec_2 & {}={} c_1\vvec_1 +0.3^2c_2\vvec_2 \\ \xvec_{4} = A\xvec_3 & {}={} c_1\vvec_1 +0.3^3c_2\vvec_2 \\ \xvec_{5} = A\xvec_4 & {}={} c_1\vvec_1 +0.3^4c_2\vvec_2 \\ \end{aligned}.

  4. Suppose that there are initially 500 bicycles at location BB and 500 at location CC. Write the vector x1\xvec_1 and find the scalars c1c_1 and c2c_2 such that x1=c1v1+c2v2\xvec_1=c_1\vvec_1 + c_2\vvec_2.

  5. Use the previous part of this problem to determine x2\xvec_2, x3\xvec_3 and x4\xvec_4.

  6. After a very long time, how are all the bicycles distributed?

Austin, Understanding Linear Algebra, §2.2 Matrix multiplication and linear combinations, Exercise 13

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Adapted from Understanding Linear Algebra © 2023 David Austin. Licensed under CC BY 4.0. Source: Understanding Linear Algebra. Imported at revision 3e6dced.