Question

If cos alpha+ cos bita = 0 = sin alpha + sin bita then cos 2alpha + cos 2bita =​

Answer 1

Step-by-step explanation:

cos2α+cos2β  

cosC+cosD=cos  

2

C+D

​  

cos  

2

C−D

​  

   

2cos(α+β)+cos(α−β)

cosα+cosβ=0=sinα+sinβ  

(cosα+cosβ)  

2

−(sinα+sinβ)  

2

=0  

cos  

2

α+cos  

2

β+2cosαcosβ−sin  

2

α−sin  

2

β−2sinαsinβ=0  

(cos  

2

α−sin  

2

α)+(cos  

2

β−sin  

2

β)=2(−sinαsinβ+cosαcosβ)  

(cos  

2

α−sin  

2

α)+(cos  

2

β−sin  

2

β)=−2cos(α+β)  

(cos2α+cos2β)=−2cos(α+β)