If x + y + z = 18 , xyz = 81and xy + yz+ zx = 90, then the value of x3 + y3 + z3 + xyz is :
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 1296
x3 + y3 + z3 - 3xyz = (x + y + z) {(x + y + z)2 - 3(xy + yz + zx)}
Putting all values in above mentioned formula
x3 + y3 + z3 - 3*81 = 18 (18*18 - 3*90)
x3 + y3 + z3 = 972 + 243 = 1215
now x3 + y3 + z3 + xyz = 1215 + 81 = 1296