Question

The sum of 6th and 7th terms of an AP is 39 and the common difference is 3, then the first term of AP is??

Answer 1

A6+A7=39

d=3

A.T.Q

a+5d+a+6d=39

2a+11d=39        

2a + 11(3)=39

2a=39-33

2a=6

a=3

Therefore the first term of the AP is 3

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Answer 2

SUM OF THE TERMS.

= 6th term + 7th term = 39
= a+5d + a+6d = 39
= 2a + 11d =39............( 1 )

DIFFERENCE OF THE TERMS.

=6th term - 7th term = 3
= a+5d - a+6d = 3
= -d = 3
= d = -3................( 2 )
put 2 in 1

=2a + 11(-3) = 39
=2a + (-33) =39
=2a -33 = 39
=2a = 39+33
=2a = 72
= a = 72/2
a=36