Arithmetic Progressions

⭐ Important Questions

1. Find 20th term of AP: 5, 9, 13, 17, ...
   Show Solution

   a=5, d=4\nT_20 = 5 + 19(4) = 5 + 76 = 81
2. Which term of AP: 21, 18, 15, ... is -81? Also find sum of terms till this term.
   Show Solution

   a=21, d=-3\nT_n = 21 + (n-1)(-3) = -81 => 21 - 3n + 3 = -81 => -3n = -105 => n=35\nS_35 = 35/2(42 + 34(-3)) = 35/2(42-102) = 35/2(-60) = -1050