Grade 8Trigonometry
Cos^2 70 +cos^2 10 -cos70.cos10 Please tell the full method how to solve this problem......
Cos^2 70 +cos^2 10 -cos70.cos10
Please tell the full method how to solve this problem......
1 Answer
Aditya Gupta
let x= Cos^2 70 +cos^2 10 -cos70.cos10
then 2x= 2Cos^2 70 +2cos^2 10 – 2cos70.cos10
2x= 1+cos140+1+cos20 – (cos80+cos60)
2x= 2 – cos40 + cos20 – cos80 – ½
2x= 3/2 +cos20 – (cos40+cos80)= 3/2 +cos20 – 2cos(120/2)cos(40/2)= 3/2 +cos20 –cos20= 3/2
so that x= 3/4
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