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a) =1-1/3+1/3-1/5+1/5-1/7+...+1/99-1/101
=1-1/101
=100/101
b) =(2/1.3+2/3.5+2/5.7+...+2/99.101).2,5
=(1-1/3+1/3-1/5+1/5-1/7+...+1/99-1/101).2,5
=(1-1/101).2,5
=100/101.2,5
=250/101
c) =(2/2.4+2/4.6+2/6.8+...+2/2008-2/2010).2
=(1/2-1/4+1/4-1/6+1/6-1/8+...+1/2008-1/2010).2
=(1/2-1/2010).2
=1004/1005
câu 1)
\(\dfrac{-12}{18}+\left(\dfrac{-21}{35}\right)=\dfrac{-19}{15}\)
câu 2)
\(-\dfrac{3}{21}+\dfrac{6}{42}=0\)
câu 3)
\(-\dfrac{18}{24}+\dfrac{15}{21}=-\dfrac{1}{28}\)
câu 4)
\(\dfrac{1}{6}+\dfrac{2}{5}=\dfrac{17}{30}\)
câu 5)
\(\dfrac{3}{5}+\left(-\dfrac{7}{4}\right)=-\dfrac{23}{20}\)
câu 6)
\(\left(-2\right)+\left(\dfrac{-5}{8}\right)=\dfrac{-21}{8}\)
câu 7)
\(\dfrac{1}{-8}+\left(-\dfrac{5}{9}\right)=-\dfrac{49}{72}\)
câu 8)
\(\dfrac{4}{13}+\dfrac{12}{39}=\dfrac{8}{13}\)
câu 9)
\(\dfrac{1}{21}+\dfrac{1}{28}=\dfrac{1}{12}\)
câu 10)
\(-\dfrac{3}{29}+\dfrac{16}{58}=\dfrac{5}{29}\)
câu 11)
\(\dfrac{8}{40}+\left(-\dfrac{36}{45}\right)=-\dfrac{3}{5}\)
câu 12)
\(-\dfrac{8}{18}+\left(-\dfrac{15}{27}\right)=-1\)
câu 13)
\(\dfrac{13}{30}+\left(-\dfrac{1}{5}\right)=\dfrac{7}{30}\)
câu 14)
\(\dfrac{2}{21}+\dfrac{1}{28}=\dfrac{11}{84}\)
câu 15)
\(5+\left(-\dfrac{3}{4}\right)=\dfrac{17}{4}\)
câu 16)
\(\dfrac{18}{24}+\dfrac{45}{-10}=-\dfrac{15}{4}\)
a) \(17-\left(-9\right)-27-19\\ =17+9-27-19\\ =\left(17-27\right)+\left(9-19\right)\\ =\left(-10\right)+\left(-10\right)=-20\)
b) \(3\cdot\left(-9\right)+9\\ =\left(-3\right)\cdot9+9\\ =9\left(-3+1\right)\\ =9\cdot\left(-2\right)=-18\)
c) \(-\left(-24\right)+\left(-37\right)-25+14\\ =24-37-25+14\\ =\left(24+14\right)-\left(37+25\right)\\ =38-62=-24\)
d) \(\left(-7\right)\cdot5-9\cdot\left(-4\right)-105\\ =\left(-7\right)\cdot5-9\cdot\left(-4\right)-21\cdot5\\ =5\left(-7-21\right)-\left(-36\right)\\ =5\cdot\left(-28\right)+36\\ =-140+36=-104\)
e) \(\left(-7\right)^2+32\div\left(-8\right)\\ =49+\left(-4\right)\\ =45\)
f) \(\left(-2\right)^2-36\div\left(-6\right)-\left|-7\right|\\ =4-\left(-6\right)-7\\ =4+6-7\\ =10-7=3\)
407 - [ (190 - 170 ): 5 + 9] : 2
407 - [ 20 : 5 + 9]:2
407 - [ 4 + 9]:2
= 407 - 6,5
= 400,5
B)TK:
+)(23.36-17.36):36
=[36.(23-17)]:36
=36.6:36
=(36:36).6
=1.6
=6
b: =23-17=6