Question : If x + y + z = 8, and x2 + y2 + z2 = 20, then the value of x3 + y3 + z3 – 3xyz is _______.
Option 1: 16
Option 2: 10
Option 3: 15
Option 4: –16
Correct Answer: –16
Solution : (x + y + z)2 = x2 + y2 + z2 + 2xy + 2yz + 2xz ⇒ 2(xy + yz + zx) = (x + y + z)2 – (x2 + y2 + z2) ⇒ 2(xy + yz + zx) = 82 – 20 = 64 – 20 = 44 $\therefore$ xy + yz + zx = 22 Now, x3 + y3 + z3 – 3xyz = (x + y + z)(x2 + y2 + z2 – xy – yz – xz) = 8(20 – 22) = –16 Hence, the correct answer is –16.
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Question : Directions: If x % y = y2 – x2, x $ y = x + y2, x # y = 2xy, then find the value of ((13 % 5) $ 6) # 15 = ?
Option 1: 480
Option 2: 720
Option 3: –360
Option 4: –3240
Question : If $x+y+z=17, x y z=171$ and $x y+y z+z x=111$, then the value of $\sqrt[3]{\left(x^3+y^3+z^3+x y z\right)}$ is:
Option 1: –64
Option 2: 4
Option 3: 0
Option 4: –4
Question : If $x^2 = y+z$, $y^2=z+x$, $z^2=x+y$, then the value of $\frac{1}{x+1}+\frac{1}{y+1}+\frac{1}{z+1}$ is:
Option 1: –1
Option 2: 1
Option 3: 2
Option 4: 4
Question : If $x+y+z=13,x^2+y^2+z^2=133$ and $x^3+y^3+z^3=847$, then the value of $\sqrt[3]{x y z}$ is:
Option 1: $8$
Option 2: $7$
Option 3: $-9$
Option 4: $-6$
Question : If $x+y+z=10$, $x y+y z+z x=25$ and $x y z=100$, then what is the value of $(x^3+y^3+z^3)$?
Option 1: 450
Option 2: 540
Option 3: 550
Option 4: 570
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