isabelle/valid/amc12b_2003_p6.thy (14 lines of code) (raw):

(* Authors: Wenda Li *) theory amc12b_2003_p6 imports Complex_Main begin theorem amc12b_2003_p6: fixes a r::real and u::"nat \<Rightarrow> real" assumes "\<forall> k. u k = a * r^k" and "u 1= 2" and "u 3=6" shows "u 0 = 2/ sqrt 3 \<or> u 0 = - 2/sqrt 3" sorry end