Question Number 27685 by NECx last updated on 13/Jan/18
$${Write}\:{the}\:{first}\:{five}\:{series}\:{indicating} \\ $$$${the}\:\mathrm{5}{th}\:{term},\mathrm{5}{th}\:{partial}\:{sum} \\ $$$$ \\ $$$$\underset{{n}=\mathrm{1}} {\overset{\infty} {\sum}}{t}_{{n}} ,\:{where} \\ $$$${t}_{{n}} =\begin{cases}{\mathrm{1}\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:{for}\:{n}=\mathrm{1}}\\{\frac{\mathrm{1}}{\mathrm{2}}\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:{for}\:{n}=\mathrm{2}}\\{\mathrm{1}−\frac{\mathrm{1}}{\mathrm{2}}+…+\left(−\mathrm{1}\right)^{{n}+\mathrm{1}} \left(\frac{\mathrm{1}}{{n}}\right)\:\:\:{for}\:\:\:{n}>\mathrm{2}}\end{cases} \\ $$
Commented by NECx last updated on 12/Jan/18
$${The}\:{three}\:{t}_{{n}} \:{are}\:{meant}\:{to}\:{be}\:{joined} \\ $$$${but}\:{I}\:{dont}\:{know}\:{how}\:{to}\:{write}\:{it} \\ $$$${with}\:{the}\:{app}\:{editor}. \\ $$
Commented by prakash jain last updated on 12/Jan/18
$$\mathrm{You}\:\mathrm{can}\:\mathrm{rows}\:\mathrm{or}\:\mathrm{columns}.\:\mathrm{press}\:\mathrm{line}\:\mathrm{and} \\ $$$$\mathrm{matrix}\:\mathrm{option}\:\mathrm{on}\:\mathrm{the}\:\mathrm{left}\:\mathrm{side}. \\ $$