Convert #cos((5x)/2)+cos((15x)/2)# into product of trigonometric ratios?

1 Answer
Shwetank Mauria
Jan 5, 2018

#cos((5x)/2)+cos((15x)/2)=2cos5xcos((5x)/2)#

Explanation:

As #cosA+cosB=2cos((A+B)/2)cos((A-B)/2)#

#cos((5x)/2)+cos((15x)/2)#

= #cos((15x)/2)+cos((5x)/2)#

= #2cos(((15x)/2+(5x)/2)/2)cos(((15x)/2-(5x)/2)/2)#

= #2cos5xcos((5x)/2)#

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