In Exercises $1825,$nd an expression for the general term

of the series and give the range of values for the index $($ or

$,$ for example$).$

$18.1$

$1=1++2+3+4+$

$19.1$

$1+=1+23+4$

$20.$ ln$(1)=2$

$23$

$34$

$4$

$21.$ ln$(1+)=2$

$2+3$

$34$

$4+5$

$5$

$22.$ sin $=3$

$3!+5$

$5!7$

$7!+$

$23.$ arctan $=3$

$3+5$

$57$

$7+$

$24.2$

$=1+2+4$

$2!+6$

$3!+8$

$4!+$

$25.2$ cos $2=26$

$2!+10$

$4!14$

$6!+$