Find the Sum of first 19terms of the A.P whose nth term is given by an

1.	Find the Sum of first 19terms of the A.P whose nth term is given by an=7-4n
Answer» Given: an=7-4nTherefore, a1 = 7-4(1)=3 a2= 7-4(2)=-1 a3 =7- 4(3)=-5A.P. will be 3,-1,-5.......d=-4Sn=n/2 (2a+(n-1)d)S19=19/2(2(3)+(19-1)-4) =-627

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