If in an AP, 8th term is 4 and 16th term is -20, then find the common

1.	If in an AP, 8th term is 4 and 16th term is -20, then find the common difference of the given AP.
Answer» Given : If in an AP, 8th term is 4 and 16th term is -20 . To Find : Common DIFFERENCE of the A.P . Solution : As Given that , $\longmapsto\tt{a+7d=4}$ $\longmapsto\tt{a+15d=-20}$ Now By Elimination Method : $\longmapsto\tt{{\not{a}}+7d=4}$ $\longmapsto\tt{{\not{a}}+15d=-20}$ $\longmapsto\tt{-8d=24}$ $\longmapsto\tt{d=\cancel\dfrac{24}{-8}}$ $\longmapsto\tt\bf{d=-<klux>3</klux>}$ So , The Common Difference of the given A.P is -3 . ____________________ ${a}_{n}$ =a + (n-1) × d General FORM = a , a + d , a + 2d ... s = n/2 [2a (n-1) × d] Here : n = nth term a = FIRST term of the a.p s = SUM of nth terms d = common difference ____________________