If the difference between two numbers is 5 and the difference between the in cubes is 1850, then the difference between their squares is:
Answer & explanation
Correct answer: option 3
Let the numbers be x and y
According to the question,
x - y = 5
x³ - y³ = 1850
We know that,
(a - b)3 = a3 - b3 - 3ab(a-b)
(5)3 = 1850 - 3ab(5)
125 = 1850 - 15ab
15ab = 1725
ab = 115
We also know that,
If x - y = n
then, x + y = \(\sqrt {n^2 + 4xy}\)
then, x + y = \(\sqrt {5^2 + 4(115)}\)
x + y = \(\sqrt {5^2 + 4(115)}\)
x + y = \(\sqrt {485}\)
The difference between their squares is = x2 - y2 = (x + y)(x - Y)
= x2 - y2 = $5\sqrt{485}$