Question

Sum of n terms of an AP is 5n2-3n.find it's tenth term.

Answer 1

Given : Sn = 5n² - 3n
S₁ = 5(1)² - 3(1)
= 5 - 3 
T₁ = 2
S₂ = 5(2)² - 3(2)
= 20 - 6 = 14
T₁ + T₂ = 14
2 + T₂ = 14
T₂ = 14 - 2
 = 12
Now, 
a = 2, d = 12 - 2 =10
T₁₀ = a + (n-1)d
T₁₀ = 2 + (10 - 1)10
T₁₀ = 2 + (9 × 10)
T₁₀ = 2 + 90
10th term = 92
Answer.