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3 years ago

Isolate the identity cos 2x - cos 8x cos 2x + cos 8x HELP PLS

Mathematics

1 answer:

Nikolay [14]3 years ago

4 0

Answer:

Cos 2x = Cos (5x-3x)

Cos(5x)Cos(3x) + Sin(5x)Sin(3x)

Cos 8x = Cos (5x + 3x)

Cos(5x)Cos(3x) - Sin(5x)Sin(3x)

Cos 2x - Cos 8x

= Cos(5x)Cos(3x) + Sin(5x)Sin(3x) -

[Cos(5x)Cos(3x) - Sin(5x)Sin(3x)]

= 2Sin(5x)Sin(3x)

Cos 2x + Cos 8x

= Cos(5x)Cos(3x) + Sin(5x)Sin(3x) +

[Cos(5x)Cos(3x) - Sin(5x)Sin(3x)]

= 2Cos(5x)Cos(3x)

= 2Sin(5x)Sin(3x) ÷ 2Cos(5x)Cos(3x)

2 gets cancelled out

Sin(5x)/Cos(5x) is Tan(5x)

Sin(3x)/Cos(3x) is Tan(3x)

Hence the fraction is identical to

Tan(5x)Tan(3x)

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