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Trig identity help (1 Viewer)

dumNerd

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Someone please do L (identity)20201107_132444.jpg
 

Randomstudent123

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for L you expand and get sin^2A+cos^2A+sin^2B+cos^2B+2sinAsinB+2cosAcosB then u use sin^2x+cos^2x=1 and
cos(A-B)=cosAcosB+sinAsinB to get 2+2(cos(A-B))then you use cos2x=2cos^2(x)-1to get 2+2(2cos^2((A-B)/2)-1)=4cos^2((A-B)/2)
 

Trebla

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For future reference, can you please post subject specific content content in subject specific forums?
 

YonOra

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How can you use the identity of Cos2x here? Or am i just being dumb
 

dumNerd

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for L you expand and get sin^2A+cos^2A+sin^2B+cos^2B+2sinAsinB+2cosAcosB then u use sin^2x+cos^2x=1 and
cos(A-B)=cosAcosB+sinAsinB to get 2+2(cos(A-B))then you use cos2x=2cos^2(x)-1to get 2+2(2cos^2((A-B)/2)-1)=4cos^2((A-B)/2)
Thank but I'm a bit confused about what happened from here 2+2(2cos^2((A-B)/2)-1) --> 4cos^2((A-B)/2)
 

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