Question

Арифметикалық прогрессия Срочно

срочно a1=2,3, d= -1,2 найдите a5

a1=- 2,1 d=-2,3 найдите a11

Answer 1

$\displaystyle\bf\\1)\\\\a_{1} =2,3\\\\d=-1,2\\\\a_{5} =a_{1} +4d=2,3+4\cdot (-1,2)=2,3-4,8=-2,5\\\\\boxed{a_{5} =-2,5}\\\\\\2)\\\\a_{1} =-2,1\\\\d=-2,3\\\\a_{11} =a_{1} +10d=-2,1+10\cdot (-2,3)=-2,1-23=-25,1\\\\\boxed{a_{11}=-25,1}$