the sum of n terms of an AP is $\displaystyle 3n^2 +5$. Find the number of terms which equals $\displaystyle 159.$
Follow Math Help Forum on Facebook and Google+
Originally Posted by banku12 the sum of n terms of an AP is $\displaystyle 3n^2 +5$. Find the number of terms which equals $\displaystyle 159.$ hi T_n=a+(n-1)d=159 ---1 We need to find a and d . a=S1=3(1)^2+5=8 $\displaystyle T_2=S_2-S_1$ $\displaystyle =3(2)^2+5-8 $ =9 so a=8 , and the common difference , d=1 . Now substitute into 1 to find n .
View Tag Cloud