51+50+49+ ..... + 21= .....A1116B1122C1128D1124Answer: A. 1116 Read Explanation: a1=51,d=−1a_1=51,d=-1a1=51,d=−1അവസാന പദം,an=21\text{അവസാന പദം}, a_n=21 അവസാന പദം,an=21n=[(an−a1)÷d]+1n = [(a_n - a_1)\div{d}] + 1n=[(an−a1)÷d]+1n=((21−51)/−1)+1=31n=((21-51)/-1)+1 =31n=((21−51)/−1)+1=31 Sn=n/2×[2a+(n−1)]×dS_n=n/2\times[2a+(n-1)]\times{d}Sn=n/2×[2a+(n−1)]×d=31/2×(2a+30d)=31/2\times(2a+30d) =31/2×(2a+30d)=31/2(102−30)=1116=31/2(102-30) =1116=31/2(102−30)=1116 Read more in App
