当a>0时
递增区间为[-c/b-π/2b+2kπ/b,-c/b+π/2b+2kπ/b],k∈Z
递减区间为[-c/b+π/2b+2kπ/b,-c/b+3π/4b+2kπ/b],k∈Z
当a0正好相反）
递增区间为[-c/b+π/2b+2kπ/b,-c/b+3π/4b+2kπ/b],k∈Z
递减区间为[-c/b-π/2b+2kπ/b,-c/b+π/2b+2kπ/b],k∈Z