Question

Decide wheather following sequence is an $A.P$ if so find the ${20}^o$ term of the progression. $-12,-5,2,9,16,23,30,.....$

Answer 1

$-12,-5,2,9,16,23,30,.............$

$d=-5-(-12)=2-(-5)=9-2=7$

Since the common difference remains the same, So, this series is in A.P.

$T_n=a+(n-1)d$

$a=-12,d=7$

$T_{20}=-12+(10-1)7$

$=-12+19\times 7$

$=121$