a , 35 * 34 + 35 * 86 + 65 * 75 + 65 * 45
= 35 * ( 34 + 86 ) + 65 * (75 + 45 )
= 35 * 120 + 65 * 120
= 120 * ( 35 + 65 )
= 120 * 100
= 12000
b , 11+12 + ...+ 20
= ( 11 +19 ) +( 12 + 18 ) + ( 13 + 17 ) + ( 14 + 16 ) +15 +20
= 30 + 30 + 30 + 30 + 15 + 20
= 30 * 4 + 35
= 120 + 35
= 155
c , 8 * 9 * 11 + 6 * 20 * 12 + 19 * 4 * 18
= 792 + 1440 + 1368
=3600
d , 143 * ( 57 - 36 ) - 57 * ( 143 - 36 )
= 143 * 57 - 143 * 36 - 57 * 143 - 57 * 36
= 143 * 57 - 57 * 143 - 143 * 36 - 57 * 36
= 0 - ( 143 - 57 )
= 0 - 86
= - 86
a) \(35.34+35.86+65.75+65.45\)
\(=35.\left(34+86\right)+65.\left(75+45\right)\)
\(=35.120+65.120\)
\(=\left(35+65\right).120\)
\(=100.120\)
\(=12000\)
b) \(11+12+...+20\)
Số số hạng của dãy là : (20 - 11) : 1 + 1 = 10 (số)
Tổng của dãy là : (20 + 1) x 10 : 2 = 105
c) \(8.9.11+6.20.12+19.4.18\)
\(=\left(8.9\right).11+\left(6.12\right).20+\left(4.18\right).19\)
\(=72.11+72.20+72.19\)
\(=72.\left(11+20+19\right)\)
\(=72.50\)
\(=3600\)
d) \(143.\left(57-36\right)-57.\left(143-36\right)\)
\(=143.57-143.36-57.143-57.36\)
\(=\left(143.57-57.143\right)-\left(143.36-57.36\right)\)
\(=0-36.\left(143-57\right)\)
\(=0-36.86\)
\(=0-3096\)
\(=-3096\)
_Chúc bạn học tốt_
a) 35.34 + 35.86 + 65 . 75 + 65 .45 = 35(34+86) + 65(75+45) = 35.120 + 65.120 = (35+65).120 = 100.120 = 12000
b)11+12+...+20 = (11+19)+(12+18)+(13+17)+(14+16)+20+15=30.4+35=120+35=155
c)8.9.11 +6.20.12+19.4.18 = 72(11+20+19) = 72 . 50 = 3600
d) 143 . (57 - 36 ) - 57.(143 - 36) = 143 . 57 - 143. 36 - 57 . 143 - 57 . 36 = 143(57 - 57) - 36(143 - 57) = 0 - 36.86 = -3096
a , 35.34+35.86+65.75+65.45\
=35.(34+86)+65.(75+45)
=35.120+65.120
=(35+65).120
= 100.120
=12000
b,11+12+...+20
=(20+1).10:2
= 105
d,143.(57-36)-57.(143-36)
=143.57-143.36-57.143-57.36
= 143.36 -57.36
=(143-57).36
=86.36
= 3096
bạn tự làm câu c nhé
