POWER(A,B)=A^B,可以嵌套
POWER(B4,2)+POWER(C4,2)=B4^2+C4^2
POWER(POWER(B4,2)+POWER(C4,2),0.5)就是上面数字B4^2+C4^2的0.5次方(根号下B4^2+C4^2)