If a − b = 4 and ab = 45, then a³ − b³ equals:

604. a³ − b³ = (a − b)³ + 3ab(a − b) = 64 + 3(45)(4) = 64 + 540 = 604. (Here a = 9 and b = 5, and 729 − 125 = 604.)

If $a - b = 4$ and $ab = 45$ , then $a^{3} - b^{3}$ equals:

Competition practiceAlgebra

a^{3} - b^{3} = (a - b)^{3} + 3 ab (a - b) = 64 + 3 (45) (4) = 64 + 540 = 604

. (Here

a = 9

and

b = 5

, and 729 − 125 = 604.)

Answer: C) 604

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