Question

Let a represent a positive number and let b represent a negative number. Tell whether each statement is True or False. True False a. The difference (a - b) could be negative. True False b. The difference (b − a) cannot be positive. True False C. The sum (a + b) could be positive. True False d. The sum (b + a) must be negative. ​

Answer 1

a. False; if b is negative, then -b is positive, so

a - b = a + (-b)

is the sum of two positive numbers, which must be positive.

b. True; the sum of two negative numbers is again negative.

c. True; a + b will be positive as long as a > |b|. (For example, if a = 2 and b = -1, then of course 2 > |-1| = 1, and a + b = 2 + (-1) = 1 > 0.)

d. False; this would contradict the result of part (c). b + a is only negative if a ≤ |b|. (For example, if a = 1 and b = -2, then b + a = -2 + 1 = -1 < 0.)