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Câu 9
a) 2/15 + (-3/5)
= 2/15 - 3/5
= 2/15 - 9/15
= -7/15
b) -5/7 + 3/7 . (-2/9)
= -5/7 - 2/21
= -15/21 - 2/21
= -17/21
c) 5/16 - (7/15 - 3/16) + 17/30
= 5/16 - 7/15 + 3/16 + 17/30
= (5/16 + 3/16) + (17/30 - 14/30)
= 1/2 + 1/10
= 5/10 + 1/10
= 6/10
= 3/5
\(a,\dfrac{2}{15}+\left(-\dfrac{3}{5}\right)\\ =\dfrac{2}{15}-\dfrac{3}{5}\\ =\dfrac{2}{15}-\dfrac{9}{15}\\ =-\dfrac{7}{15}\\ b,-\dfrac{5}{7}+\dfrac{3}{7}\times\left(-\dfrac{2}{9}\right)\\ =-\dfrac{5}{7}-\dfrac{2}{21}\\ =-\dfrac{15}{21}-\dfrac{2}{21}\\ =-\dfrac{17}{21}\\ c,\dfrac{5}{16}-\left(\dfrac{7}{15}-\dfrac{3}{16}\right)+\dfrac{17}{30}\\ =\dfrac{5}{16}-\dfrac{7}{15}+\dfrac{3}{16}+\dfrac{17}{30}\\ =\left(\dfrac{5}{16}+\dfrac{3}{16}\right)-\left(\dfrac{17}{15}+\dfrac{17}{30}\right)\\ =\dfrac{1}{2}-\dfrac{17}{10}\\ =\dfrac{5}{10}-\dfrac{17}{10}\\ =-\dfrac{6}{5}.\)
`a,5 xx (-7)+(-2) xx (-5)`
`=5 xx (-7)+5 xx 2`
`= 5 xx (2-7)`
`=5 xx (-5)`
`=-25`
`b,5 xx (-9)+(-2) xx 3`
`=3 xx (-15)+3 xx (-2)`
`=3 xx (-15-2)`
`=3 xx (-17)`
`=-51`
`c,6 xx (-5)^2+3 xx (-15)`
`=2 xx 3 xx 25+3 xx (-15)`
`=3 xx 75-3 xx 15`
`=3 xx (75-15)`
`=3 xx 60`
`=180`
Thực hiện các phép tính(tính nhanh nếu có thể)
a)135-12.(3+6)
b)36+4.(7-15)
c) (-3)2 .23
d)(-6-14):(-5)
a, 135 - 12 . 9
= 135 - 108
= 27
b, 36 + 4 . -8
= 36 + (-32)
= 36 - 32
= 4
c, (-3)2 . 23
= 9 . 8
= 72
d, ( -6 - 14 ) : (-5) = (-21) : (-5) = 4,2
a 135-12*(3+6)
= 135 - 12*9
= 135 - 12*(10-1)
=135- (12*10-12*1
)=135-(120-12)
=135-108
=27
b= 35+4*-8
=35+ 4*(-10+2)
=35+(4*-10+4*2)
=35+(-40+8)
=35+-32
=3
\(49,=\dfrac{38}{5}-\left(\dfrac{19}{7}+\dfrac{28}{5}\right)\)
\(=\dfrac{38}{5}-\dfrac{19}{7}-\dfrac{28}{5}\)
\(=\left(\dfrac{38}{5}-\dfrac{28}{5}\right)-\dfrac{19}{7}\)
\(=2-\dfrac{19}{7}=-\dfrac{5}{7}\)
\(50,=\dfrac{25}{81}.\dfrac{15}{22}=\dfrac{125}{594}\)
mik xinloi ạ câu 50 mik viết sai đề nên mong bạn giải lại giúp ạ <3
a)=-7/21+8/24
=-1/3+1/3
=0
b)=-3/5.(2/7+5/7)+23/5
=-3/5.7/7+23/5
=-3/5.1+23/5
=-3/5+23/5
=20/5=4
c)=75/100-11/2+5/10:5/12+1/4
=3/4-11/2+1/2:5/12+1/4
=3/4+-11/2+1/2.12/5+1/4
=3/4+-22/4+6/5+1/4
=-19/4+6/5+1/4
=(-19/4+1/4)+6/5
=-18/4+6/5
=-9/2+6/5
=-45/10+12/10
=-23/10
\(a.36+15+64\\ =\left(36+64\right)+15\\ =100+15\\ =115\\ b.12\cdot36+12\cdot64\\ =12\cdot\left(36+64\right)\\ =12\cdot100\\ =1200\\ c.\left(3^2+2^3\cdot5\right):7\\ =\left(9+8\cdot5\right):7\\ =\left(9+40\right):7\\ =49:7\\ =7\)\(\)
\(a,36+15+64\)
\(=\left(36+64\right)+15=100+15\)
\(=115\)
\(b,12.36+12.64\)
\(=12.\left(36+64\right)=12.100\)
\(=1200\)
\(c,\left(3^2+2^3.5\right):7\)
=\(\left(9+8.5\right):7\)
\(=49:7=7\)