The nth termof an AP is given by-4n+15.find the sum of first 20 terms

1.	The nth termof an AP is given by-4n+15.find the sum of first 20 terms
Answer» A1=-4(1)+15=11, A2=-4(2)+15=7 , D=7-11=-4. S20=20/2(22+19(-4))=10(22-76)=10(-54)=-540 95 an=-4n+15a1=-4×1+15 =11a2=-4×2+15 =7CD=7-11 =-4a20=a+19d =11+19×-4 =11-76 =-65 May be..... 18

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