Answer:
½√2
Step-by-step 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)
