一条关于三角函数的题目
来源:学生作业帮 编辑:搜搜做题作业网作业帮 分类:数学作业 时间:2024/07/15 08:45:10
一条关于三角函数的题目
![](http://img.wesiedu.com/upload/3/a6/3a6d0b537c59d3c6f161cd25517e3ab1.jpg)
第五题咋写?
![](http://img.wesiedu.com/upload/3/a6/3a6d0b537c59d3c6f161cd25517e3ab1.jpg)
第五题咋写?
![一条关于三角函数的题目](/uploads/image/z/16151156-44-6.jpg?t=%E4%B8%80%E6%9D%A1%E5%85%B3%E4%BA%8E%E4%B8%89%E8%A7%92%E5%87%BD%E6%95%B0%E7%9A%84%E9%A2%98%E7%9B%AE)
tanC(cosA/sinA +cosB/sinB)
=(sinC/cosC) * sin(A+B)/sinAsinB
=(sinC)^2/(sinAsinBcosC)=1
由正弦定理,
(sinC)^2/(sinAsinBcosC)=c^2/abcosC=1
即 c^2=abcosC
由余弦定理,(a^2+b^2)/c^2 -1 =(a^2+b^2-c^2)/c^2=2abcosC/c^2=2
所以(a^2+b^2)/c^2=3
=(sinC/cosC) * sin(A+B)/sinAsinB
=(sinC)^2/(sinAsinBcosC)=1
由正弦定理,
(sinC)^2/(sinAsinBcosC)=c^2/abcosC=1
即 c^2=abcosC
由余弦定理,(a^2+b^2)/c^2 -1 =(a^2+b^2-c^2)/c^2=2abcosC/c^2=2
所以(a^2+b^2)/c^2=3