Question

How do you do this question?

Answer 1

½√2

Explanation:

∑ₙ₌₀°° (-1)ⁿ π²ⁿ / (4²ⁿ (2n)!)

∑ₙ₌₀°° (-1)ⁿ (π/4)²ⁿ / (2n)!

Using the Taylor expansion for cos x:

cos (π/4)

½√2