Question

if the sum of first n term of an AP is 3n²/2-4n
find the 15th term and Ap.​

Answer 1

Answer:

Step-by-step explanation:

Tn     =$S_{n}$  −$S_{n-1}$     .(1)

Now $S_{n}$   =$3n^{2}$ +4n

∴$S_{n-1}$=$(3n-1)^{2}$  +4(n−1)=$3n^{2}$ −2n−1

∴Tn =($3n^{2}$−4n)−($3n^{2}$  −2n−1), by (1)

=6n+1

∴$T_{1}$  =7,  $T_{2}$  =13,  $T_{3}$   =19,______

∴a=7,d=6.