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cosx+cosy+cos(x+y)=3/2....relation btw x and y?

cosx+cosy+cos(x+y)=3/2....relation btw x and y?

Grade:11

3 Answers

Arun Kumar IIT Delhi
askIITians Faculty 256 Points
7 years ago
Hello Student,
Correct question is
cosx+cosy-cos(x+y)=3/2
2cos((x+y)/2)cos((x-y)/2)-2[cos((x+y)/2))]^2-0.5=0
=>2ka-2k^2-0.5=0
=>D=4a^2-4>=0
=>a=1 since its a cos(x-y) whose value is in [-1,1]
so x=y
You got what you asked for.
Thanks & Regards
Arun Kumar
Btech, IIT Delhi
Askiitians Faculty
Abhinav Acharya
20 Points
7 years ago
Please explain me how you have eliminated 3/2 ?? Thanks sir!!
Arun Kumar IIT Delhi
askIITians Faculty 256 Points
7 years ago
Hello Abhinav,
See 2cos^2A=1+cos2A
so
cos(2A)=2cos^2A-1
if 2A=x+y
then
cos(x+y)=2cos((x+y)/2^2-1
Now please try putting it in the equation.
Thanks & Regards
Arun Kumar
Btech, IIT Delhi
Askiitians Faculty

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