Question Details

If x + y + z = 1 , x y + y z + z x = 1 and x y z = 1 , then ( x3 + y3 + z3 ) is equal to _____ .

Options

A

1

B

3

C

2

D

0

Show Answer

Correct Answer :

Option A

1

Solution :

The correct answer is 1.

To find the value of x3+y3+z3, we use the standard algebraic identity relating the sum of cubes to the sum of variables, the sum of pairwise products, and their product:

x3+y3+z3-3xyz=(x+y+z)[(x2+y2+z2)-(xy+yz+zx)]

Step 1: Calculate x2+y2+z2

We start with the expansion formula for the square of a trinomial:

(x+y+z)2=x2+y2+z2+2(xy+yz+zx)

Rearranging the terms to solve for x2+y2+z2:

x2+y2+z2=(x+y+z)2-2(xy+yz+zx)

Substitute the given values x+y+z=1 and xy+yz+zx=-1 into the equation:

x2+y2+z2=(1)2-2(-1)

x2+y2+z2=1+2=3

Step 2: Evaluate x3+y3+z3

Now substitute x+y+z=1, xy+yz+zx=-1, xyz=-1, and x2+y2+z2=3 into the main algebraic identity:

x3+y3+z3-3(-1)=(1)[3-(-1)]

x3+y3+z3+3=1×(3+1)

x3+y3+z3+3=4

x3+y3+z3=4-3

x3+y3+z3=1

Thus, x3+y3+z3 is equal to 1.

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