Question

In an AP if the common difference the equal to minus 4 and the 7th term A7 is 4 then find the first term.

Answer 1

d=-4

a7=4
a+6d=4
a+6(-4)=4
a-24=4
a=4+24
a=28

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Answer 2

First value of the series is 28.

Solution:

According to the arithmetic progression the formula to find $n^{th}$ term is $\bold{T_{n}=a+(n-1) d}$

a = first term in the series.

n = Number of terms present in the series.

$T_{n}$ = the term that is to be found out or given.

d = the common difference between two numbers of the series.

Now putting the value of d = -4 and $a_{7}$ = 4

We get 4 = a + ( 7 - 1 ) ( -4 )

a = 28.