Question

Find the sum of all odd numbers from 1 to 2019

Answer 1

`S_n=(n(a_1+a_n))/(2)\\a_1=1\\a_n=2019\\d=2\\n=?\\\\a_n=a_1+(n-1)d\\2019=1+(n-1)\cdot2\\2n-2=2018\\2n=2020\\n=1010\\\\S_(1010)=(1010(1+2019))/(2)\\S_(1010)=505\cdot2020\\S_(1010)=1020100`