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\(2021S=2021+2021^2+2021^3+...+2021^{40}\\ 2021S-S=2021+2021^2+2021^3+...+2021^{40}-1-2021-2021^2-...-2021^{39}\\ 2020S=2021^{40}-1\\ S=\dfrac{2021^{40}-1}{2020}\)
\(\text{a)A=2021+{750-[2021-(+50)}\)
\(A=2021+750-2021+50\)
\(A=\left(2021-2021\right)+\left(750+50\right)\)
\(A=0+800\)
\(A=800\)
\(\text{b)B=-215.[19+(-1236)]+215.(19-236)}\)
\(B=-215.19+215.1236+215.19-215.236\)
\(B=19.\left(-215+215\right)+215.\left(1236-236\right)\)
\(B=19.0+215.1000\)
\(B=0+215000\)
\(B=215000\)
học tốt
a, [ 13-17 ].[-10]+[-7]0
=-4.[-10]+1
=40+1
=41
b, 72.[28-49] + 28.[-49-72]
=72.[-21]+28.[-121]
=-1512+[-3388]
=-4900
c, -65.[87-17] - 87.[17-65]
=-65.70-87.[-48]
=4550-[-4276]
=8726
d, -23.63+23.21-58.23
=23.(-63)+23.21-58.23
=23.(-63+23-58)
=23.(-40-58)
=23.(-98)
=-2254
e, 25.134+25.[-34]
=25.[134+(-34)]
=25.100
=2500
\(4\cdot5^2-3^2\cdot\left(2021^0+3^2\right)\)
\(=4\cdot25-9\cdot\left(1+9\right)\)
\(=100-9\cdot10\)
\(=100-90\)
\(=10\)
4. 52- 32. ( 20210+ 32)
= 4 . 25 - 9 . ( 1 + 9 )
= 100 - 9 . 10
= 100-90
= 10
\(a,-215-358+215+\left(-42\right)\\ =\left(-215+215\right)+\left(-358-42\right)\\ =0-400\\ =-400\\ b,13\cdot\left(23+22\right)-3\cdot\left(17+28\right)\\ =13\cdot45-3\cdot45\\ =45\cdot\left(13-3\right)\\ =45\cdot10\\ =450\)
A) 150-[102-(14-11)2 .20210
=150-[102-32.20210 ]
=150-[100-9.1]
=150-91
= 59
\(215-\left(-85\right)-2021^0+\left(28-100\right)-\left(28+2021\right)\)
\(=215+85-1+28-100-28-2021\)
\(=\left(215+85-100\right)-1+\left(28-28\right)-2021\)
\(=200-1+0-2021\)
\(=199-2021=-1822\)