20+15+20+28
cach tinh nhanh
K
Khách
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VN
1
15 tháng 11 2015
4+8+12+16+20+24+28
= (16+24)+(28+12)+20+4+8
= 40+40+20+12
= 112
10 tháng 8 2015
khoảng cách: 2-1=1
số số hạng là: (20-1):1+1=20(số)
tổng là: (20+1)x20:2=210
AP
0
R
4
NA
9 tháng 11 2021
( 5 + 10 + 15 + 20 + 25 + 30 + 35 ) x ( 42 - 6 x 7 )
= ( 5 + 10 + 15 + 20 + 25 + 30 + 35 ) x ( 42 - 42 )
= ( 5 + 10 + 15 + 20 + 25 + 30 + 35 ) x 0
= 0
S
22 tháng 3 2017
\(\frac{5.4^{15}.9^9-4.3^{20}.8^9}{5.2^9.6^{19}-7.2^{29}.27^6}\)
\(=\frac{5.\left(2^2\right)^{15}.\left(3^2\right)^9-2^2.3^{20}.\left(2^3\right)^9}{5.2^9.\left(2.3\right)^{19}-7.2^{29}.\left(3^3\right)^6}\)
\(=\frac{5.2^{30}.3^{18}-2^2.3^{20}.2^{27}}{5.2^9.2^{19}.3^{19}-7.2^{29}.3^{18}}\)
\(=\frac{5.2^{30}.3^{18}-2^{29}.3^{20}}{5.2^{28}.3^{19}-7.2^{29}.3^{18}}\)
\(=\frac{2^{29}.3^{18}.\left(5.2-3^2\right)}{2^{28}.3^{18}.\left(5.3-7.2\right)}\)
\(=\frac{2^{29}.3^{18}.1}{2^{28}.3^{18}.1}\)
\(=\frac{2^{29}}{2^{28}}=2\)
13 tháng 3 2017
A.\(\dfrac{4}{20}\)+\(\dfrac{16}{42}\)+\(\dfrac{6}{15}\)+\(\dfrac{-3}{5}\)+\(\dfrac{2}{21}\)+\(\dfrac{-10}{21}\)+\(\dfrac{3}{20}\)
=\(\dfrac{1}{5}\)+\(\dfrac{8}{21}\)+\(\dfrac{6}{15}\)+\(\dfrac{-3}{5}\)+\(\dfrac{2}{21}\)+\(\dfrac{-10}{21}\)+\(\dfrac{3}{20}\)
=\((\dfrac{1}{5}\)+\(\dfrac{6}{15}\)+\(\dfrac{-3}{5}\)\()\)+\((\dfrac{8}{21}\)+\(\dfrac{2}{21}\)+\(\dfrac{-10}{21}\)\()\)+\(\dfrac{3}{20}\)
=\((\)\(\dfrac{1}{5}\)+\(\dfrac{2}{5}\)+\(\dfrac{-3}{5}\)\()\)+ 0 +\(\dfrac{3}{20}\)
= 0 + 0 +\(\dfrac{3}{20}\)
=\(\dfrac{3}{20}\)
B.\(\dfrac{42}{46}\)+\(\dfrac{250}{286}\)+\(\dfrac{-2121}{2323}\)+\(\dfrac{-125125}{143143}\)
=\(\dfrac{21}{23}\)+\(\dfrac{125}{143}\)+\(\dfrac{-21}{23}\)+\(\dfrac{-125}{134}\)
=\((\dfrac{21}{23}+\dfrac{-21}{23})+(\dfrac{125}{143}+\dfrac{-125}{134})\)
= 0 + 0
= 0
Chúc bạn Tran Mai học tốt nha
ND
1
4 tháng 4 2015
\(\frac{14}{15}\div\frac{7}{20}=\frac{14}{15}\times\frac{20}{7}=\frac{14\times20}{15\times7}=\frac{8}{3}\)
\(\frac{9}{8}\div\frac{27}{16}=\frac{9}{8}\times\frac{16}{27}=\frac{9\times16}{8\times27}=\frac{2}{3}\)
(20+20)+(15+28)
=40+42
=82