AB=AC,BD=BC,且∠A=36°,且AB=根号5+1/2,求AD

Question

AB=AC,BD=BC,且∠A=36°,且AB=根号5+1/2,求AD

Answer 1

利用余弦定理可知：
BC^2=AB^2+AC^2-2*AB*AC*cosA=2.85,故BC=BD=1.69
CD^2=BC^2+BD^2-2*BC*BD*cosA=1.08,故CD=1.04
所以,AD=AC-CD=1.7