(sinx)'=cosx=sin(x+π/2)
(sinx)''=[sin(x+π/2)]'=cos[x+(π/2)]=sin[x+2(π/2)]
……
（sinx)^(n)=[sin(x+(n-1)(π/2))]'=cos[x+(n-1)(π/2)]=sin[x+n(π/2)]