Question

In an A.P, first term=a, difference is d, last term is L, find the term before last

Answer 1

Given: first term=a, difference is d, last term is L

To find:  the term before last term in AP.

Solution:

• Now we have given that:

                first term = a

                common difference = d

                last term = l

• Let the number of terms be n.

                Then a(n) = l

• We know the formula:

                a(n) = a + (n-1)d

• So we get:

                a + (n-1)d = l

                (n-1)d = l - a

                n - 1 = (l - a) / d

                n = (l - a) / d + 1

                n = (l - a + d) / d

                n-1 =  (l - a + d) / d - 1

                n - 1 = (l - a)/d

Answer:

         So the second last term is (l - a)/d.

Answer 2

Step-by-step explanation:

An=a+(n-1)d=L

The term before last is An-1

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

=a+(n-2)d

=l-d