Ta có :
TH1 :\(\left\{{}\begin{matrix}\text{ZB - ZA = 9}\\\text{ ZA + ZB = 19 }\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}\text{ZA = 5 (Bo)}\\\text{ZB = 14 ( Si) }\end{matrix}\right.\)
TH2:\(\left\{{}\begin{matrix}\text{ZB - ZA = 7}\\\text{ZA + ZB = 19}\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}\text{ZA = 6 (C)}\\\text{ZB = 13 ( Al )}\end{matrix}\right.\)