Bài 2: 

Lũy thừa với số mũ chẵn của một số hữu tỉ âm là số dương

Lũy thừa với số mũ lẻ của một số hữu tỉ âm là số âm

Bài 8:

a: \(2^{27}=8^9\)

\(3^{18}=9^9\)

Bài 13:

a: \(x^3=343\)

nên x=7

b: \(\left(2x-3\right)^2=9\)

\(\Leftrightarrow\left[{}\begin{matrix}2x-3=3\\2x-3=-3\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\\x=0\end{matrix}\right.\)

a: \(A=\dfrac{4^2\cdot4^3}{2^{10}}=\dfrac{4^5}{2^{10}}=1\)

b: \(C=\dfrac{5^4\cdot20^4}{25^5\cdot4^5}=\dfrac{100^4}{100^5}=\dfrac{1}{100}\)

Bài 9:
a: \(10^8\cdot2^8=20^8\)

b: \(10^8:2^8=5^8\)

c: \(25^4\cdot2^8=100^4\)

d: \(27^2:25^3=\left(\dfrac{9}{25}\right)^3\)

Bài 4: 

a: \(x:\left(-\dfrac{1}{2}\right)^3=-\dfrac{1}{2}\)

\(\Leftrightarrow x=\dfrac{-1}{2}\cdot\dfrac{-1}{8}\)

hay \(x=\dfrac{1}{16}\)

b: \(\left(\dfrac{3}{4}\right)^3\cdot x=\left(\dfrac{3}{4}\right)^7\)

\(\Leftrightarrow x=\left(\dfrac{3}{4}\right)^7:\left(\dfrac{3}{4}\right)^3=\left(\dfrac{3}{4}\right)^4=\dfrac{81}{256}\)

a: \(A=2\left(2x+x^2\right)-x^2\left(x+2\right)+x^3-4x+3\)

\(=4x+2x^2-x^3-2x^2+x^3-4x+3\)

=3

b: B=z(y-x)+y(z-x)+x(y+z)-2yz+100

=yz-xz+yz-xy+xy+xz-2yz+100

=100

c: \(C=2y\left(y^2+y+1\right)-2y^2\left(y+1\right)-2\left(y+10\right)\)

\(=2y^3+2y^2+2y-2y^3-2y^2-2y-20\)

=-20

d: \(D=x\left(3x+12\right)-\left(7x-20\right)+x^2\left(2x-3\right)-x\left(2x^2+5\right)\)

\(=3x^2+12x-7x+20+2x^3-3x^2-2x^3-5x\)

=(12x-7x-5x)+20

=20

e: E=3(2x-1)-5(x-3)+6(3x-4)-19x

=6x-3-5x+15+18x-24-19x

=(6x-5x+18x-19x)+(-3+15-24)

=12-24

=-12

f: F=(4x-5)(2x+3)-4(x+2)(2x-1)+10x+7

\(=8x^2+12x-10x-15-4\left(2x^2-x+4x-2\right)+10x+7\)

\(=8x^2+2x-15-4\left(2x^2+3x-2\right)+10x+7\)

\(\)\(=8x^2+12x-8-8x^2-12x+8\)

=0

g: G=(7x-6y)(4x+3y)-2(14x+y)(x-9y)-19(13xy-1)

\(=28x^2+21xy-24xy-18y^2-2\left(14x^2-126xy+xy-9y^2\right)\) -247xy+19

=\(28x^2-3xy-18y^2-28x^2+250xy+18y^2-247xy+19\)

=19

a: 14/-42=-1/3

-16/64=-1/4

18/72=1/4

-20/120=-1/6

b: -12/45=-4/15=-8/30=-16/60=-20/75=-25/90

help

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