Question #3d3b0

1 Answer
Psykolord1989 .
Oct 9, 2017

#10(cos^2x-sin^2x)-5#

Explanation:

The double angle formula for #cos 2x# is #cos 2x = cos^2x-sin^2x#. With that in mind...

#10cos2x -5 = 10(cos^2x-sin^2x)-5#

To derive the double angle formula for #cos2x#, instead rewrite it as #cos(x+x)#, and use the sum of two angles formula:

#cos(a+b)=cosacosb - sinasinb#

And set a=b=x

#cosxcosx-sinxsinx = cos^2x - sin^2x#

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