Integral derivative:
arctanX = X—X * 3/3+X * 5/5-……+(- 1)*(n— 1)X[X *(2n— 1)]/[2n— 1]+……
Take x =1;
π/4 = 1— 1/3+ 1/5—……+(- 1)*(n— 1)[ 1/(2n— 1)]+……
You can get it.
Where * stands for power, x stands for symbol and x stands for the letter X.