If the topic is f`(x)= 1-2sinx, let f`(x)=0, that is, there is x = X The tangent at is parallel to the X axis. At this time, sinx= 1/2, so x=kπ π/6 or kπ 5π/6, so the first four terms are π, 5π/6, π π/6 and π 5π/6 respectively. Add up to get 6π.

Mobile phone typing, hope to adopt!