package cap3

// Ex1 例题1
// 求1/1! - 1/3! + 1/5! - 1/7! + ... + (-1)^(n+1)/(2n-1)!
func Ex1(n int) float64 {
    sum, fab := 0.0, uint64(1)
    for i := 1; i <= n; i++ {
        fab *= 2*uint64(i) + 1
        if i%2 == 0 {
            sum += -1.0 / float64(fab)
        } else {
            sum += 1.0 / float64(fab)
        }
    }

    return sum
}