x=-20736的四次方根在复数范围开方,用三角式。在复数范围开n方,开n次方有个根。-20736=(12^4)(cosπ+isinπ)x(k)=-20736的四次方根 =12[cos(πk/2+π/4)+isin(kπ/2+π/4)]k=0,1,2,3x=12[cos(π/4)+isin(π/4)]=6√2+(6√2)ix₁=12[cos(3π/4)+isin(3π/4)]=-6√2+(6√2)ix₂=12[cos(5π/4)+isin(5π/4)]=-6√2-(6√2)ix₃=12[cos(7π/4)+isin(7π/4)]=6√2-(6√2)i在复数范围计算不用添加±号(-20736)^(1/4)=√√(-20736)=√(144i)=6√2+(6√2)i