If x + y + z = 11 and xy + yz + zx = 42 then the value of x² + y² + z² is:

x + y + z = 11

xy + zx + yz = 42

​$$(x + y + z)^2 = x^2 + y^2 + z^2 + 2(xy + yz + zx)$$​​

Can be written as,

​$$x^2 + y^2 + z^2 = (x + y + z)^2 - 2(xy + yz + zx)$$​​

Substitute the values into the identity:

​$$x^2 + y^2 + z^2 = (11)^2 - 2 \times 42 = 121 - 84 = 37$$​​

Thus, the value of $$x^2 + y^2 + z^2$$ is 37.