Question

In an ap sum of first n terms is 4n-n2.find its 10term

Answer 1

Answer:

Step-by-step explanation:

Sn = 4n-n2 put n = 1 we get S1 = 4×1 - 1×1 = 4 - 1 = 3 S1 = a1 (first term)=3 put n = 2 we get S2 = 4 × 2 - 2 × 2 = 8 - 4 = 4 S2 = a1 + a2(sum of first 2 terms) 4 = 3 + a2 (S2 = 4 and a1 = 3) 4 - 3 = a2 Now a2 = 1 and a1 =3 and common diffrence d = a2 - a1 d = 1 - 3 = -2 Now we need to a10 a10= a + 9d = 3 + 9×-2 =3-18= -15 Hence 10th term of Ap is -15