The sum of the squares of three numbers is 138, while the sum of their products taken two at a time is 131. Their sum is:
Question: The sum of the squares of three numbers is 138, while the sum of their products taken two at a time is 131. Their sum is:
[A].
20
30
40
None of these
[A].
[B].
[C].
[D].
Answer: Option A
Explanation:
Let the numbers be a, b and c.
Then, a2 + b2 + c2 = 138 and (ab + bc + ca) = 131.
(a + b + c)2 = a2 + b2 + c2 + 2(ab + bc + ca) = 138 + 2 x 131 = 400.
(a + b + c) = 400 = 20.
Video Explanation: https://youtu.be/qmJ-0X8j_xQ