the third , 20th and the last terms of an a.p. are 6.5 ,57.5 and 87.5 find the frist term.comman difference and the number of term
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third term=6.5 ⇒a + 2d=6.5₋₋₋₋₋₋₋₋₋)1)
twenty term=57.5 ⇒a +19d=57.5₋₋₋₋₋₋₋₋(2)
by eliminating method solve the equation (1) and (2):
a+2d =6.5
a+19d=57.5
₋ ₋ ₋
₋₋₋₋₋₋₋₋₋₋₋₋₋₋₋₋
17d=51
d =3
putting the value a in equation (1):
a+2d=6.5
a+2(3)=6.5
a+6=6.5
a=0.5
twenty term=57.5 ⇒a +19d=57.5₋₋₋₋₋₋₋₋(2)
by eliminating method solve the equation (1) and (2):
a+2d =6.5
a+19d=57.5
₋ ₋ ₋
₋₋₋₋₋₋₋₋₋₋₋₋₋₋₋₋
17d=51
d =3
putting the value a in equation (1):
a+2d=6.5
a+2(3)=6.5
a+6=6.5
a=0.5
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