How to find the sum of the first n terms of an = 1 / n

How to find the sum of the first n terms of an = 1 / n

Only less than or more than can be obtained by the method of expansion and contraction, but not the accurate value
You can change 1 / N to 1 / (√ n * √ n), and then enlarge or reduce the denominator to 1 / (√ n * (√ n + 1)), 1 / (√ n * (√ n-1)), and then use the split term elimination method to find the limit. Note that: √ (n) + 1

The countdown of a sequence
An = P * A / Q * a + P. it's written in the note that this is the reciprocal method. What does this mean and how to use it

An = P * A / Q * a + P, the reciprocal method is, write 1 / a 1 / a = Q * a + P / P * a = q / P + 1 / a 1 / a - 1 / a = q / P, the following should be what you can understand, so don't write it

Find the limit of (e ^ x-1-x) / (√ (1-x) - cos √ (x)) when x tends to zero

In 0 / 0 type limit, the numerator and denominator are derived at the same time, and then 0 is substituted in. If it is still 0 / 0, the numerator and denominator are derived again until the denominator is not 0