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a) 20- ( -40 ) +10 b) - 21+ ( -13 ) -4
= ( 40+ 20 ) +10 = - ( 21+13 )- 4
= 60+ 10 = ( -34 ) - 4
= 70 = - ( 34+ 4 )
= - 38
c) ( 3-23 ) - ( 4- 10 ) d) ( -8 + 15 ) - ( -6-20)
= ( - 20 ) - ( -6 ) = 7+ - 26
= - ( 20+ 6 ) = -19
= - 26
\(\text{a) }20-\left(-40\right)+10=20+40+10=60+10=70\)
\(\text{b) }-21+\left(-13\right)-4=-25-13-4=-38-4=-42\)
\(\text{c) }\left(3-23\right)-\left(4-10\right)=3-23-4+10=-20+6=-14\)
\(\text{d) }\left(-8+15\right)-\left(-6-20\right)=-8+15+6+20=-8+41=33\)
20 - ( - 40 ) + 10 ....................
= 20 + 40 + 10..............
= 60 + 10 = 70...........
Bài làm
a,20-(-40)+10 b,-21+(-13)-4 c,(3-23)-(4-10) d,(-8+15)-(-6-20)
= 20 + 40 + 10 = - 24 - 4 = -20 - ( -6 ) = 7 + 26
= 70 = -28 = -14 = 31
# Chúc bạn học tốt #
B1:
a,-14 - 7 + x = -12
7 + x =(-12 + -14)
7 + x = -26
x = -26 -7
x -33
b,
b
x + (-15) - (- 6) = 11
x + (-15) =11 + ( -6)
x + (-15) =5
x =5 - (-15)
x = 20
\(B=\frac{1}{1\cdot2\cdot3}+\frac{1}{2\cdot3\cdot4}+\frac{1}{3\cdot4\cdot5}+\frac{1}{18\cdot19\cdot20}\)
\(B=\frac{1}{2}\left(\frac{2}{1\cdot2\cdot3}+\frac{2}{2\cdot3\cdot4}+\frac{2}{3\cdot4\cdot5}+\frac{2}{18\cdot19\cdot20}\right)\)
\(B=\frac{1}{2}\left(\frac{1}{1\cdot2}-\frac{1}{2\cdot3}+\frac{1}{2\cdot3}-\frac{1}{3\cdot4}+\frac{1}{3\cdot4}-\frac{1}{4\cdot5}+...+\frac{1}{18\cdot19}-\frac{1}{19\cdot20}\right)\)
\(B=\frac{1}{2}\left(\frac{1}{1\cdot2}-\frac{1}{19\cdot20}\right)\)
\(B=\frac{1}{2}\cdot\frac{189}{380}=\frac{189}{760}\)
\(C=\frac{52}{1\cdot6}+\frac{52}{6\cdot11}+\frac{52}{11\cdot16}+...+\frac{52}{31\cdot36}\)
\(C=\frac{52}{5}\left(\frac{5}{1\cdot6}+\frac{5}{6\cdot11}+\frac{5}{11\cdot16}+...+\frac{6}{31\cdot36}\right)\)
\(C=\frac{52}{5}\left(1-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+\frac{1}{11}-\frac{1}{16}+...+\frac{1}{31}-\frac{1}{36}\right)\)
\(C=\frac{52}{5}\cdot\left(1-\frac{1}{36}\right)\)
\(C=\frac{91}{9}\)
a) 70 c) - 38
c) - 26 d) - 19
a) 20 - (-40) + 10 = 20 + 40 + 10 = 70
b) -21 + (-13) - 4 = -21 - 13 - 4 = -38
c) (3 - 23) - (4 - 10) = -20 - 4 + 10 = -14
d) (-8 + 15) - (-6 - 20) = 7 + 6 + 20 = 33