Question

In the sequence an = 7n - 5, what is 3a7 - 9a9 ?

Answer 1

Answer:

390 is the Answer

Step-by-step explanation:

an = 7n - 5

now,

a(1) = 7(1) - 5

    = 7 - 5

    =  2

a(2) = 7(2) - 5

      = 14 - 5

      = 9

d =  a2 - a1

 =  9 - 2

 = 7

a7 = a + ((n-1)d)

   =  2 + 6(7)

   = 2 + 42

   = 44

3a7 = 3(44)

       = 132

a9 = a + ((n-1)d)

    = 2 + 8(7)

    = 2 + 56

    = 58

9a9 = 9(58)

       = 522

NOW ,

9a9 - 3a7 = 522 - 132

                = 390