Plxxxx see this image,,.....que 9 and 10.....fast....
Tanisha , 5 Years ago
Grade 11
Trigonometry> Plxxxx see this image,,.....que 9 and 10....
1 Answers
Arun
Last Activity: 5 Years ago
Dear student
please ask only one question in one thread.
9.
Cos^2α+cos^2(α+β)-2cosαcosβcos(α+β)
=cos^2α+cos^2(α+β)-{cos(α+β)+cos(α-β) }cos(α+β)
=cos^2α+cos^2(α+β)-{cos^2(α+β)+cos(α-β)*cos(α+β)}
=cos^2α+cos^2(α+β)-cos^2(α+β)-cos(α-β)*cos(α+β)}
=cos^2α-cos(α-β)*cos(α+β)
=cos^2α+cos^2(α+β)-{cos(α+β)+cos(α-β) }cos(α+β)
=cos^2α+cos^2(α+β)-{cos^2(α+β)+cos(α-β)*cos(α+β)}
=cos^2α+cos^2(α+β)-cos^2(α+β)-cos(α-β)*cos(α+β)}
=cos^2α-cos(α-β)*cos(α+β)
=cos^2α-cos^2α+sin^2β
=sin^2β
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