Question

求过程！！！！！帮帮忙谢谢！！！！

Answer 1

S=1/2absinC=(c^2-a^2-b^2)/4√3
sinC=(c^2-a^2-b^2)/2√3ab 平方一下
sin^2 C=(c^2-a^2-b^2)^2/12a^2b^2=1-cos^2 C 1
cosC=(a^2+b^2-c^2)/2ab
cos^2 C=(a^2+b^2-c^2)^2/4a^2b^2 2
2式代入1式得
(c^2-a^2-b^2)^2/12a^2b^2=1-(a^2+b^2-c^2)^2/4a^2b^2
(c^2-a^2-b^2)^2=12a^2b^2-3(a^2+b^2-c^2)^2
(a^2+b^2-c^2)^2=12a^2b^2-3(a^2+b^2-c^2)^2
(a^2+b^2-c^2)^2=3a^2b^2
a^2+b^2-c^2=ab√3
(a^2+b^2-c^2)/2ab=√3/2=cosC
C=30

Answer 2

S=(c²-a²-b²)/(4√3)----------------------(1)
cosC=(a²+b²-c²)/(2ab)
ab=(1/2)(a²+b²-c²)/cosC
S=(1/2)absinC
=(1/4)(a²+b²-c²)*tanC------------------(2)
联立(1)(2)
tanC=-1/√3
∠C=150°

Answer 3

六十度

追答