7.(2019山东禹城第一中学高二期中考试)如图,在长方-|||-体 -(A)_(1)(B)_(1)(C)_(1)(D)_(1) 中,O为AC的中点.-|||-(1)化简: overrightarrow ({A)_(1)O}-dfrac (1)(2)overrightarrow (AB)-dfrac (1)(2)overrightarrow (AD)-|||-(2)设E是棱DD1上的点,且 overrightarrow (DE)=dfrac (2)(3)overrightarrow (D{D)_(1)} 若 overrightarrow (EO)=xoverrightarrow (AB)+-|||-overrightarrow (AD)+zoverrightarrow (A{A)_(1)} 试求实数x、y、z的值-|||-D-|||-C1-|||-A-|||-E-|||-B-|||-D. C-|||-A B