please help

[winter briar]

One message removed from a suspended account.

[polar wyvern]

1. Ask your question and show the work you've done so far. If you've posted a screenshot of a question, specify which part you need help with.
2. Wait patiently for a helper to come along.
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   +close
   

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[quasi wadi]

Did you try expanding each one?

[quasi wadi]

@winter briar

[fallen loom]

Use formula for sum of geometric progression Σ(cosθ)^2n = 1/(1-cos(θ)^2)

[fast oasis]

Each one is an infinite gp and the series is convergent as sin and cos lie in the interval (0,1) here