
Bradford T. answered 03/21/21
Retired Engineer / Upper level math instructor
an = (-1)n/(2n)!
1/0! = 1.0
-1/2! = -0.5
1/4! = 0.04166
-1/6! = -0.001388
1/8! = 0.0000248 which is less than 0.0001 error, so more terms won't contribute much
Sum = 1 - 0.5 + 0.04166 - 0.001388 + 0.0000248 ≈ 0.5403