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A,-3/-7+5/19+-4/7
=(-3/-7+-4/7)+5/19
=-1/7+5/19=16/133
B,-13/24+-5/24+7/21
=-3/4+7/21=-5/12
C,-5/13+(-8/13+1)
=(-5/13+-8/13)+1
=-1+1=0
D,2/3+(3/8+-2/3)
=(2/3+-2/3)+3/8
=0+3/8=3/8
E,(-3/4+5/8)+-1/8
=-1/8+1/8=0
\(\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+...+\frac{1}{49\cdot50}\)
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{5}-.....+\frac{1}{49}-\frac{1}{50}\)
\(=\frac{1}{2}-\frac{1}{50}\)
\(=\frac{24}{50}=\frac{12}{25}\)
\(\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+...+\frac{1}{49\cdot50}\)
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{49}-\frac{1}{50}\)
\(=\frac{1}{2}-\frac{1}{50}\)
\(=\frac{12}{25}\)
a, \(7^{2010}:7=7^{2009}\)
b, \(4^{20}:4^0=4^{20}\)
c, \(\frac{3^8.3^{15}}{3^7.3^{14}}=\frac{3^{23}}{3^{21}}=3^2\)
d, \(\frac{4^{16}.4^2}{4^{20}:4^2}=\frac{4^{18}}{4^{18}}=4^0\)
e, \(\frac{2^{15}:2^{10}}{2^{18}:2^{15}}=\frac{2^5}{2^3}=2^2\)
f, \(25^4:125=\left(5^2\right)^4:5^3=5^8:5^3=5^5\)
33-(-4).(-7)+32.10=89.
Chúc bạn học giỏi.
33 - ( - 4 ) . ( - 7 ) + 32 . 10
= 27 - 28 + 90
= - 1 + 90
= 89