src/HOL/Analysis/Complex_Transcendental.thy
changeset 64240 eabf80376aab
parent 63918 6bf55e6e0b75
child 64267 b9a1486e79be
equal deleted inserted replaced
64239:de5cd9217d4c 64240:eabf80376aab
  1313     by simp
  1313     by simp
  1314 next
  1314 next
  1315   case False
  1315   case False
  1316   then have "z / of_real(norm z) = exp(\<i> * of_real(Arg z))"
  1316   then have "z / of_real(norm z) = exp(\<i> * of_real(Arg z))"
  1317     using Arg [of z]
  1317     using Arg [of z]
  1318     by (metis abs_norm_cancel nonzero_mult_divide_cancel_left norm_of_real zero_less_norm_iff)
  1318     by (metis abs_norm_cancel nonzero_mult_div_cancel_left norm_of_real zero_less_norm_iff)
  1319   then have "- z / of_real(norm z) = exp (\<i> * (of_real (Arg z) - pi))"
  1319   then have "- z / of_real(norm z) = exp (\<i> * (of_real (Arg z) - pi))"
  1320     using cis_conv_exp cis_pi
  1320     using cis_conv_exp cis_pi
  1321     by (auto simp: exp_diff algebra_simps)
  1321     by (auto simp: exp_diff algebra_simps)
  1322   then have "ln (- z / of_real(norm z)) = ln (exp (\<i> * (of_real (Arg z) - pi)))"
  1322   then have "ln (- z / of_real(norm z)) = ln (exp (\<i> * (of_real (Arg z) - pi)))"
  1323     by simp
  1323     by simp
  1916 lemma csqrt_exp_Ln:
  1916 lemma csqrt_exp_Ln:
  1917   assumes "z \<noteq> 0"
  1917   assumes "z \<noteq> 0"
  1918     shows "csqrt z = exp(Ln(z) / 2)"
  1918     shows "csqrt z = exp(Ln(z) / 2)"
  1919 proof -
  1919 proof -
  1920   have "(exp (Ln z / 2))\<^sup>2 = (exp (Ln z))"
  1920   have "(exp (Ln z / 2))\<^sup>2 = (exp (Ln z))"
  1921     by (metis exp_double nonzero_mult_divide_cancel_left times_divide_eq_right zero_neq_numeral)
  1921     by (metis exp_double nonzero_mult_div_cancel_left times_divide_eq_right zero_neq_numeral)
  1922   also have "... = z"
  1922   also have "... = z"
  1923     using assms exp_Ln by blast
  1923     using assms exp_Ln by blast
  1924   finally have "csqrt z = csqrt ((exp (Ln z / 2))\<^sup>2)"
  1924   finally have "csqrt z = csqrt ((exp (Ln z / 2))\<^sup>2)"
  1925     by simp
  1925     by simp
  1926   also have "... = exp (Ln z / 2)"
  1926   also have "... = exp (Ln z / 2)"