Question

Find S30 for the series 25+20+15...

Answer 1

\[\large t_1=25\]\[\large \text{common difference } \space d=-5\]
compute t30 using the formula for the arithmetic sequence \[\large t_{n}=t_1+(n-1)d\] then find the sum S30 using \[\large S_n=\frac{ 1 }{ 2 }n(t_1+t_n)\]

Answer 2

thanks bro

Answer 3

YW