Question

10,13,16.....is an AS. Find xn, X20, check whether 80 is a term ?​

Answer 1

Answer:

xₙ = 3n+7

x₂₀= 67

also 80 is not a term..

Explanation:

sequence is 10,13,16,................

common difference, d = 13-10 = 3

first term,f = 10

xₙ = dn+(f-d)

   = 3×n + (10-3)

   = 3n+7

to find x₂₀ , apply n=20 in 3n+7

x₂₀= 3×20 + 7

    = 60+7

    = 67

To know whether a number is a term or not , subtract first term from that number , and check whether the result is the multiple of common difference. If the difference is a multiple of d then it is a term...

consider xₙ = 80

             f    = 10

       xₙ - f    = 80-10 =70

70 is not divisible by common difference 3 , so 80 is not a term of this sequence.....

Hope this answer will help u.....