964 CHAPTER 9 Systems and Matrices 88. (Modeling) Predator-Prey Relationship In certain parts of the Rocky Mountains, deer provide the main food source for mountain lions. When the deer population is large, the mountain lions thrive. However, a large mountain lion population reduces the size of the deer population. Suppose the fluctuations of the two populations from year to year can be modeled with the matrix equation c mn+1 dn+1d = c 0.51 -0.05 0.4 1.05d c mn dnd . The numbers in the column matrices give the numbers of animals in the two populations after n years and n + 1 years, where the number of deer is measured in hundreds. (a) Give the equation for dn+1 obtained from the second row of the square matrix. Use this equation to determine the rate at which the deer population will grow from year to year if there are no mountain lions. (b) Suppose we start with a mountain lion population of 2000 and a deer population of 500,000 (that is, 5000 hundred deer). How large would each population be after 1 yr? 2 yr? (c) Consider part (b) but change the initial mountain lion population to 4000. Show that the populations would both grow at a steady annual rate of 1.01. 89. Northern Spotted Owl Population Refer to Exercise 87(b). Show that the number 0.98359 is an approximate zero of the polynomial represented by 3 -x 0.18 0 0 -x 0.71 0.33 0 0.94 - x3 . 90. Predator-Prey Relationship Refer to Exercise 88(c). Show that the number 1.01 is a zero of the polynomial represented by 2 0.51 - x -0.05 0.4 1.05 - x2 . Use the following matrices, where all elements are real numbers, to show that each statement is true for 2 * 2 matrices. A = c a11 a21 a12 a22d , B = c b11 b21 b12 b22d , and C = c c11 c21 c12 c22d . 91. A + B = B + A (commutative property) 93. 1AB2C = A1BC2 (associative property) 95. c1A + B2 = cA + cB, for any real number c. 97. 1cA2d = 1cd2A, for any real numbers c and d. 92. A + 1B + C2 = 1A + B2 + C (associative property) 94. A1B + C2 = AB + AC (distributive property) 96. 1c + d2A = cA + dA, for any real numbers c and d. 98. 1cd2A = c1dA2, for any real numbers c and d.
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