Answer:
Step-by-step explanation:
Using the addition formulae for cosine
cos(x ± y) = cosxcosy ∓ sinxsiny
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cos(120 + x) = cos120cosx - sin120sinx
= - cos60cosx - sin60sinx
= - cosx -
sinx
squaring to obtain cos² (120 + x)
= cos²x +
sinxcosx +
sin²x
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cos(120 - x) = cos120cosx + sin120sinx
= -cos60cosx + sin60sinx
= - cosx +
sinx
squaring to obtain cos²(120 - x)
= cos²x -
sinxcosx +
sin²x
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Putting it all together
cos²x + cos²x +
sinxcosx +
sin²x +
cos²x -
sinxcosx +
sin²x
= cos²x + cos²x +
sin²x
= cos²x +
sin²x
= (cos²x + sin²x) =