Mathematics
The sum of two whole numbers is 7 and the sum of their cubes is 133, find the sum of their squares.
Answer
Let two numbers be x and y.
Given,
The sum of two whole numbers is 7 and the sum of their cubes is 133.
x + y = 7 and x3 + y3 = 133
By formula,
⇒ x3 + y3 = (x + y)3 - 3xy(x + y)
⇒ 133 = 73 - 3xy × 7
⇒ 133 = 343 - 21xy
⇒ 21xy = 343 - 133
⇒ 21xy = 210
⇒ xy = 10.
By formula,
⇒ (x + y)2 = x2 + y2 + 2xy
⇒ 72 = x2 + y2 + 2 × 10
⇒ 49 = x2 + y2 + 20
⇒ x2 + y2 = 49 - 20
⇒ x2 + y2 = 29.
Hence, sum of squares of numbers = 29.