Toán `Tính bằng cách hợp lí a/1+3+5+7+9+…+2013 b/100+98+96+…+2-97-95-…-1 c/1+2+3+4+…+n d/2.3.12+4.6.42+8.27.3 20/07/2021 By Ayla `Tính bằng cách hợp lí a/1+3+5+7+9+…+2013 b/100+98+96+…+2-97-95-…-1 c/1+2+3+4+…+n d/2.3.12+4.6.42+8.27.3
a) 1+3+5+7+…+2013 =(2013+1)+(2011+3)+…+(1009+1005)+1007 =2014+2014+…+2014+1007 =2014*1007+1007 =2015*1007 =2 029 105 b)100+98+96+…+2-97-95-…-1 =(98-97)+(96-95)+…+(2-1)+100 =1+1+1+…+1+100 =1*49+100 =49+100 =149 c)1+2+3+4+…+n =(n+1)+(n-1+2)+(n-2+3)+… =n+1+n+1+n+1+… d)2.3.12+4.6.42+8.27.3 =(2*12)*3+(4*6)*42+(8*3)*27 =24*3+24*42+24*27 =24*(3+27+42) =24*72 =1728 Trả lời