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a. 3/5 . 15/7 - 15/7 . 8/5
= 15/7(3/5-8/5)
=15/7. -\(\frac{1}{1}\)
=22/7
b. 4/5 . 1 3/7 + 4/5 . 4/7
=4/5(13/7+4/7)
=4/5.17/7
= 68/35
a,\(15-\left(-4-x\right)=6\)
\(\Leftrightarrow-4-x=15-6\)
\(\Leftrightarrow-4-x=9\)
\(\Leftrightarrow x=-4-9\)
\(\Leftrightarrow x=-13\)
b,\(-30+\left(25-x\right)=-1\)
\(\Leftrightarrow25-x=-1-\left(-30\right)\)
\(\Leftrightarrow25-x=29\)
\(\Leftrightarrow x=25-29=-4\)
c,\(x-\left(12-25\right)=-8\)
\(\Leftrightarrow x+13=-8\)
\(\Leftrightarrow x=-21\)
e,\(x-5=1\Rightarrow x=6\)
g,\(x+30=-4\)
\(\Leftrightarrow x=-4-30\)
\(\Leftrightarrow x=-34\)
h,\(x-\left(-24\right)=3\)
\(\Leftrightarrow x+24=3\)
\(\Leftrightarrow x=3-24\)
\(\Leftrightarrow x=-21\)
i,\(\left(x+5\right)+\left(x-9\right)=x+2\)
\(\Leftrightarrow x+5+x-9-x-2=0\)
\(\Leftrightarrow x-6=0\)
\(\Leftrightarrow x=6\)
k,\(\left(27-x\right)+\left(15+x\right)=x-24\)
\(\Leftrightarrow27-x+15+x-x+24=0\)
\(\Leftrightarrow-x+66=0\)
\(\Leftrightarrow-x=-66\)
\(\Leftrightarrow x=66\)
a) 15-(-4-x)=6
15 + 4 + x = 6
19 + x = 6
x = 6 - 19
x = 6 + ( -19 )
x = -13
b) -30+( 25- x ) =-1
25- x = -1 - ( - 30 )
25- x = -1 + 30
25- x =29
x = 25 - 29
x = 25 + ( -29 )
x = -4
c) x- ( 12-25) =-8
x - ( - 13 ) = -8
x + 13 = -8
x = -8 - 13
x = -8 + ( -13 )
x = - 21
d) ( x-29 ) - (17- 38 ) = -9
( x-29) - (-21 ) = -9
x -29 = -9 + ( -21 )
x -29 = -30
x = -30 + 29
x = -1
e) x-5=1
x = 1 + 5
x = 6
g) x + 30 = -4
x = -4 - 30
x = -4 + ( -30 )
x = -34
h) x- ( -24 ) = 3
x = 3 + ( -24 )
x = -21
l) 22- ( - x ) = 12
-x = 22 - 12
-x = 10
x = -10
i) ( x + 5 ) + ( x - 9 ) = x + 2
x + 5 + x - 9 = x + 2
x + x + ( 5 - 9 ) = x + 2
x + x + ( -4 ) = x + 2
x + x = x + 2 - ( -4 )
x + x = x + 2 + 4
x + x =x + 6
=> x = 6
*tính nhanh
=1*27*25*3+27*25-25*11
=25*(1*27*3+27-11)
=25*97=2425
mình chỉ làm được ý thôi nhá
bài 1 :
a) S1=( 1 + 3 - 5 - 7 )+(9+11-13-15)+...+(393+395-397-399)
S1=(-8)+(-8)+...+(-8)
S1=(-8)*199
S1=-1592
b)S2=(1-2-3+4)+( 5 - 6 - 7 +8)+...+( 97 - 98 - 99 + 100)
S2=0+0+...+0
S2=0*100
S2=0
phần c và d tương tự nhé
BÀI 2
c)<=>2(x-1)+4 chia hết x-3
=>8 chia hết x-3
=>x-3\(\in\){-1,-2,-4,-8,1,2,4,8}
=>x\(\in\){2,1,-1,-5,4,5,7,11}
\(a,\frac{7}{15}-\frac{22}{60}=\frac{7\cdot4}{60}-\frac{22}{60}=\frac{28}{60}-\frac{22}{60}=\frac{6}{60}=\frac{1}{10}\)
\(b,\frac{37}{40}-\frac{64}{100}=\frac{37}{40}-\frac{16}{25}=\frac{185}{200}-\frac{128}{200}=\frac{57}{200}\)
\(c,130\frac{25}{8}-120\frac{17}{8}\)
\(=130+\frac{25}{8}-120+\frac{17}{8}\)
\(=130-120+\left[\frac{25}{8}+\frac{17}{8}\right]\)
\(=130-120+\frac{21}{4}\)
\(=10+\frac{21}{4}=10+5\frac{1}{4}=(10+5)+\frac{1}{4}=15\frac{1}{4}\)
Ba câu kia tương tự
a)\(\frac{7}{15}-\frac{22}{60}=\frac{7}{15}-\frac{11}{30}=\frac{14}{30}-\frac{11}{30}=\frac{14-11}{30}=\frac{3}{30}=\frac{1}{10}\)
b)\(\frac{37}{40}-\frac{64}{100}=\frac{37}{40}-\frac{16}{25}=\frac{185}{200}-\frac{128}{200}=\frac{185-128}{200}=\frac{57}{200}\)
c)\(130\frac{25}{8}-120\frac{7}{8}=\left(130+\frac{25}{8}\right)-\left(120+\frac{7}{8}\right)=130+\frac{25}{8}-120-\frac{7}{8}\)\(=\left(130-120\right)+\left(\frac{25}{8}-\frac{7}{8}\right)=10+\frac{25-7}{8}=10+\frac{18}{8}=10+\frac{9}{4}\)\(=10+2\frac{1}{4}=10+2+\frac{1}{4}=12+\frac{1}{4}=12\frac{1}{4}\)
d)\(1-\frac{1}{2}-\frac{1}{3}-\frac{1}{6}=1-\left(\frac{1}{2}+\frac{1}{3}+\frac{1}{6}\right)=1-\left(\frac{3}{6}+\frac{2}{6}+\frac{1}{6}\right)=1-\frac{6}{6}=1-1=0\)
e)\(\frac{17}{8}-\frac{11}{6}+\frac{2}{9}=\frac{153}{72}-\frac{132}{72}+\frac{16}{72}=\frac{153-132+16}{72}=\frac{37}{72}\)
f)\(\frac{21}{21}+\frac{18}{69}+\frac{3}{5}=1+\frac{6}{23}+\frac{3}{5}=\frac{115}{115}+\frac{30}{115}+\frac{69}{115}=\frac{115+30+69}{115}=\frac{214}{115}\)