Question

Find S16 for 1 + 7 + 13 + 19 +

Answer 1

`S_n=(a_1+a_n)/(2)\cdot n\\n=16\\a_1=1\\a_(16)=?\\\\a_n=a_1+(n-1)\cdot d\\d=6\\a_(16)=1+(16-1)\cdot6=1+90=91\\\\S_(16)=(1+91)/(2)\cdot6=46\cdot6=276`