If $A=\left {x\epsilon C: x^2=1\right }$ and $B=\left {x\epsilon C: x^4=1\right }$, then $A\Delta B$ is equal to
$\left {-1, 1\right }$
$\left {-1, 1, i, -i\right }$
$\left {-i, i\right }$
None of these
$x^2=1\Rightarrow x=-1, 1.\therefore A=\left {-1, 1\right }$$x^4=1\Rightarrow x^2=-1, 1$$\Rightarrow x=-i, i, -1, 1.\therefore B=\left {-i, i, -1, 1\right }$$\therefore A\Delta B=(A-B)\cup (B-A)=\phi \cup \left {-i, i\right }=\left {-i, i\right }$.