Question

find the 7th term from the end of AP 11 ,15..107

Answer 1

A1=11, A2=15,......
d=A1-A2
d=11-15=4

A7=A+(n-1)d
=11+(7-1)4
=11+6*4
=11+24
=35

.°. A7=35

Answer 2

Given,

AP = 11,15,......107.

a = 11.
D = a2 - a1 = 15 - 11 = 4.
an = 107.

By using the formula,
an = a + (n-1) D

107 = 11 + (n - 1) 4

107 = 11 + (4n - 4)

107 = 7 + 4n

107 - 7 = 4n

100 = 4n

n = 100/4

n = 25.

Therefore, the number of terms = 25.

The 7th term from the end of the AP = 19th term.

a19 = a + (n - 1) D

a19 = 11 + (19 - 1) 4

a19 = 11 + (18)4

a19 = 11 + 72

a19 = 83.

Therefore the 7th term from the end of the AP is 83.

:)