$f(x)=1+2(sinx-\frac{1}{2}sin2x+\frac{1}{3}sin3x-\frac{1}{4}sin4x+$cdots$)f(x)=1+x,-.$ Answer: $f(x)=1+2(sinx-\frac{1}{2}sin2x+\frac{1}{3}sin3x-\frac{1}{4}sin4x+$cdots$)$

In each of the following problems you are given a function on the interval $-$pif$($x$)=1+2($sinx$-(1)/(2)$sin$2$x$+(1)/(3)$sin$3$x$-(1)/(4)$sin$4$x$+$cdots$)$f$($x$)=1+$x$,-\backslash$pi $.$ Answer: f$($x$)=1+2($sinx$-(1)/(2)$sin$2$x$+(1)/(3)$sin$3$x$-(1)/(4)$sin$4$x$+$cdots$)$