a+1/a = a+(5a-a^2)/a = a+5-a=5(a+1/a)^2 = a^2+1/a^2+2=25a^2+1/a^2 = 23
a^2-5a+1=0两边同时除以a，得：a-5+1/a=0a+1/a=5a^2+1/a^2=(a+1/a)^2-2=25-2=23
