a) A=625–(61–17).12+(27+27):17A=625–(61–17).12+(27+27):17

=625–528+3=100=625–528+3=100

b) B=−126–(42–5)2+870:29B=−126–(42–5)2+870:29

=−126–112+30=−126–112+30

=−126–121+30=−217

a: \(=625-44\cdot12+\dfrac{41}{17}=97+\dfrac{41}{17}=\dfrac{1690}{17}\)

b: \(=-126-11^2+30=-126-121+30=-217\)

\(A=625-\left(61-17\right)\cdot12+\left(27+24\right)\div17\)

\(A=625-44\cdot12+51\div17\)

\(A=625-528+3\)

\(A=100\)

\(B=-126-\left(4^2-5^2\right)+870-29\)

\(B=-126-\left(16-25\right)+870-29\)

\(B=-126-\left(-9\right)+870-29\)

\(B=-117+870-29\)

\(B=753-29\)

\(B=724\)

           Chúc bn hok tốt

1) A \(=625-\left(61-17\right).12+\left(27+24\right):17\)

\(\Leftrightarrow A=625-44.12+51:17\)

\(\Leftrightarrow A=625-528+3\)

\(\Leftrightarrow A=100\)

Vậy A = 100

2) B \(=-126-\left(4^2-5^2\right)+870-29\)

\(\Leftrightarrow B=-126-\left(16-25\right)+870-29\)

\(\Leftrightarrow B=-126-16+25+870-29\)

\(\Leftrightarrow B=724\)

Vậy B = 724

a) \(A=625-\left(61-17\right).12+\left(27+24\right):17\)

\(=625-44.12+51:17\)

\(=625-528+3=100\)

b) \(B=-126-\left(4^2-5^2\right)+870-29\)

\(=-126-16+25+870-29\)

\(=724\)

Bài 1 :

a, 25 + (-42) = - ( 42 - 25 ) = - 17

b, (-17) + 5 + 8 + 17 + (-3 )

= [ (-17) + 17 ] + [ ( 5 + 8 ) + (-3) ]

= 0 + 10

= 10

c, 25. 2² - ( 15-18 ) + ( 12 - 19 + 10 )

= 25 . 4 - (-3) + 3

= 100 - [ (-3) + 3 ]

= 100 - 0

= 100

d, 120 - 35 + 29 - 242

= 85 + 29 - 242

= 114 - 242

= -128

1/

a, 24 - {12 -[(-10)-(-2)]}

=24-{12-(-8)}

=24-20

=4

b,\(\frac{2}{3}\)+\(\frac{1}{3}\).(\(\frac{-2}{3}\)+\(\frac{5}{6}\)):\(\frac{2}{3}\)

=\(\frac{2}{3}\)+\(\frac{1}{3}\).(\(\frac{-4}{6}\)+\(\frac{5}{6}\)):\(\frac{2}{3}\)

=\(\frac{2}{3}\)+\(\frac{1}{3}\).\(\frac{1}{6}\).\(\frac{3}{2}\)

=\(\frac{2}{3}\)+\(\frac{1}{18}\).\(\frac{3}{2}\)

=\(\frac{2}{3}\)+\(\frac{1}{6}\).\(\frac{1}{2}\)

=\(\frac{2}{3}\)+\(\frac{1}{12}\)

=\(\frac{8}{12}\)+\(\frac{1}{12}\)

=\(\frac{9}{12}\)=\(\frac{3}{4}\)

2/

a,\(\frac{-2}{5}\)+(\(\frac{-5}{9}\)+\(\frac{2}{5}\))

=\(\frac{-2}{5}\)+\(\frac{-5}{9}\)+\(\frac{2}{5}\)

=(\(\frac{-2}{5}\)+\(\frac{2}{5}\))+\(\frac{-5}{9}\)

=         0+\(\frac{-5}{9}\)

=          \(\frac{-5}{9}\)

Các bạn nhớ ghi cách làm ra nhé!

Bài 6 :

a) \(\dfrac{625}{5^n}=5\Rightarrow\dfrac{5^4}{5^n}=5\Rightarrow5^{4-n}=5^1\Rightarrow4-n=1\Rightarrow n=3\)

b) \(\dfrac{\left(-3\right)^n}{27}=-9\Rightarrow\dfrac{\left(-3\right)^n}{\left(-3\right)^3}=\left(-3\right)^2\Rightarrow\left(-3\right)^{n-3}=\left(-3\right)^2\Rightarrow n-3=2\Rightarrow n=5\)

c) \(3^n.2^n=36\Rightarrow\left(2.3\right)^n=6^2\Rightarrow\left(6\right)^n=6^2\Rightarrow n=6\)

d) \(25^{2n}:5^n=125^2\Rightarrow\left(5^2\right)^{2n}:5^n=\left(5^3\right)^2\Rightarrow5^{4n}:5^n=5^6\Rightarrow\Rightarrow5^{3n}=5^6\Rightarrow3n=6\Rightarrow n=3\)

Bài 7 :

a) \(3^x+3^{x+2}=9^{17}+27^{12}\)

\(\Rightarrow3^x\left(1+3^2\right)=\left(3^2\right)^{17}+\left(3^3\right)^{12}\)

\(\Rightarrow10.3^x=3^{34}+3^{36}\)

\(\Rightarrow10.3^x=3^{34}\left(1+3^2\right)=10.3^{34}\)

\(\Rightarrow3^x=3^{34}\Rightarrow x=34\)

b) \(5^{x+1}-5^x=100.25^{29}\Rightarrow5^x\left(5-1\right)=4.5^2.\left(5^2\right)^{29}\)

\(\Rightarrow4.5^x=4.25^{2.29+2}=4.5^{60}\)

\(\Rightarrow5^x=5^{60}\Rightarrow x=60\)

c) Bài C bạn xem lại đề

d) \(\dfrac{3}{2.4^x}+\dfrac{5}{3.4^{x+2}}=\dfrac{3}{2.4^8}+\dfrac{5}{3.4^{10}}\)

\(\Rightarrow\dfrac{3}{2.4^x}-\dfrac{3}{2.4^8}+\dfrac{5}{3.4^{x+2}}-\dfrac{5}{3.4^{10}}=0\)

\(\Rightarrow\dfrac{3}{2}\left(\dfrac{1}{4^x}-\dfrac{1}{4^8}\right)+\dfrac{5}{3.4^2}\left(\dfrac{1}{4^x}-\dfrac{1}{4^8}\right)=0\)

\(\Rightarrow\left(\dfrac{1}{4^x}-\dfrac{1}{4^8}\right)\left(\dfrac{3}{2}+\dfrac{5}{3.4^2}\right)=0\)

\(\Rightarrow\dfrac{1}{4^x}-\dfrac{1}{4^8}=0\)

\(\Rightarrow\dfrac{4^8-4^x}{4^{x+8}}=0\Rightarrow4^8-4^x=0\left(4^{x+8}>0\right)\Rightarrow4^x=4^8\Rightarrow x=8\)

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