Consider C = {x : x − 5 = 0} and E = {x : x is an integral positive root of x² − 2x − 15 = 0}. Then
AC ≠ E because C is the empty set
BC ≠ E because E has two elements
CC = D = E for D = {x : x² = 25}
DC = E only
Answer & Solution
Correct answer: D. C = E only
C = {5}. The equation x² − 2x − 15 = 0 has roots x = 5 and x = −3; the integral POSITIVE root is just 5, so E = {5}. Hence C = E. D = {−5, 5} has two elements, so D ≠ E.
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