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Aptitude · Q462

Algebra

Competitive Exams · Aptitude · question 462

Q462

If x + y + z = 17, xyz = 171 and xy + yz + zx = 111, then the value of 3 ( x^3 + y^3 + z^3 + xyz ) is:

If x + y + z = 17, xyz = 171 and xy + yz + zx = 111, then the value of     is:
A.
-64
B.
0
C.
4
D.
-4
Answer

Answer: Option D

Solution

Answer: Option D
Solution:
x3 + y3 + z3 - 3xyz = (x + y + z)[x2 + y2 + z2 - (xy + yz + zx)]
(x + y + z)2 = x2 + y2 + z2 + 2(xy + yz + zx)
289 = x2 + y2 + z2 + 2 × 111
x2 + y2 + z2 = 67
Now,
x3 + y3 + z3 - 3xyz = 17(67 - 111)
x3 + y3 + z3 - 3xyz = -44 × 17
x3 + y3 + z3 - 3xyz + 4xyz = -748 + 4xyz
x3 + y3 + z3 + xyz = -748 + 4 × 171
x3 + y3 + z3 + xyz = -748 + 684
x3 + y3 + z3 + xyz = -64