tan(a+b)=2 sinc等于多少.当a=1c=根号5时.b为多少
问题描述:
tan(a+b)=2 sinc等于多少.当a=1c=根号5时.b为多少
答
tan(a+b)=2
tanC=-2
sinC/cosC=-2
sin^2C=4cos^2C
sin^2C = 4/5
sinC = 2√5/5
cosC = -√5/5
由余弦定理:
c^2=a^2+b^2-2abcosC
5 = 1+b^2+2√5/5b
整理
5b^2+2√5b-20=0
b=(√105-√5)/5