Xét ΔEDI có \(\widehat{EIF}\) là góc ngoài

nên \(\widehat{EIF}=\widehat{IED}+\widehat{IDE}\)

=>\(\widehat{IED}=110^0-90^0=20^0\)

EI là phân giác của góc DEF

=>\(\widehat{DEF}=2\cdot\widehat{DEI}=40^0\)

ΔDEF vuông tại D

=>\(\widehat{DEF}+\widehat{DFE}=90^0\)

=>\(\widehat{DFE}=90^0-40^0=50^0\)

 cảm ơn bạn nhiều nha

Sửa đề: \(\dfrac{2^{12}\cdot3^5-4^6\cdot9^2}{2^{12}\cdot9^6+8\cdot9^5}\)

\(=\dfrac{2^{12}\cdot3^5-2^{12}\cdot3^4}{2^{12}\cdot3^{12}+2^3\cdot3^{10}}\)

\(=\dfrac{2^{12}\cdot3^4\left(3-1\right)}{2^3\cdot3^{10}\left(2^9\cdot3^2+1\right)}\)

\(=\dfrac{2^9}{3^6}\cdot\dfrac{2}{1028\cdot9+1}=\dfrac{2^{10}}{729\left(1028\cdot9+1\right)}\)

sorry mình ấn nhầm nha

Trong tập hợp T, những phần tử có số ngày 31 là

\(T=\) { tháng 10; tháng 12 }

giúp với...

Bài 2:

a: \(\left|x+\dfrac{1}{5}\right|-\dfrac{1}{2}=\dfrac{9}{10}\)

=>\(\left|x+\dfrac{1}{5}\right|=\dfrac{1}{2}+\dfrac{9}{10}=\dfrac{14}{10}=\dfrac{7}{5}\)

=>\(\left[{}\begin{matrix}x+\dfrac{1}{5}=\dfrac{7}{5}\\x+\dfrac{1}{5}=-\dfrac{7}{5}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{6}{5}\\x=-\dfrac{8}{5}\end{matrix}\right.\)

b: \(\dfrac{5}{4}-3\left|2x+5\right|=\dfrac{3}{4}\)

=>\(3\left|2x+5\right|=\dfrac{5}{4}-\dfrac{3}{4}=\dfrac{2}{4}=\dfrac{1}{2}\)

=>\(\left|2x+5\right|=\dfrac{1}{6}\)

=>\(\left[{}\begin{matrix}2x+5=\dfrac{1}{6}\\2x+5=-\dfrac{1}{6}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}2x=\dfrac{1}{6}-5=-\dfrac{29}{6}\\2x=-\dfrac{1}{6}-5=-\dfrac{31}{6}\end{matrix}\right.\)

=>\(\left[{}\begin{matrix}x=-\dfrac{29}{12}\\x=-\dfrac{31}{12}\end{matrix}\right.\)

c: \(\left(\dfrac{3}{5}x+\dfrac{1}{2}\right)^2=\dfrac{25}{16}\)

=>\(\left[{}\begin{matrix}\dfrac{3}{5}x+\dfrac{1}{2}=\dfrac{5}{4}\\\dfrac{3}{5}x+\dfrac{1}{2}=-\dfrac{5}{4}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\dfrac{3}{5}x=\dfrac{5}{4}-\dfrac{1}{2}=\dfrac{3}{4}\\\dfrac{3}{5}x=-\dfrac{5}{4}-\dfrac{1}{2}=-\dfrac{7}{4}\end{matrix}\right.\)

=>\(\left[{}\begin{matrix}x=\dfrac{3}{4}:\dfrac{3}{5}=\dfrac{5}{4}\\x=-\dfrac{7}{4}:\dfrac{3}{5}=-\dfrac{7}{4}\cdot\dfrac{5}{3}=-\dfrac{35}{12}\end{matrix}\right.\)

d: \(3-\left(2x+1\right)^2=2\)

=>\(\left(2x+1\right)^2=3-2=1\)

=>\(\left[{}\begin{matrix}2x+1=1\\2x+1=-1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=-1\end{matrix}\right.\)

Bài 1:

a: \(\left(-\dfrac{2}{3}\right)^2\cdot\dfrac{9}{16}-\sqrt{\dfrac{4}{81}}:\dfrac{16}{9}+\left|-0,25\right|\)

\(=\dfrac{4}{9}\cdot\dfrac{9}{16}-\dfrac{2}{9}\cdot\dfrac{9}{16}+\dfrac{1}{4}\)

\(=\dfrac{4}{16}-\dfrac{2}{16}+\dfrac{1}{4}=\dfrac{1}{2}-\dfrac{1}{8}=\dfrac{3}{8}\)

b: \(\left(-2\right)^3+\dfrac{1}{2}:\dfrac{1}{8}-\sqrt{25}+\left|-8\right|\)

\(=-8+\dfrac{1}{2}\cdot8-5+8\)

=4-5=-1

c: \(\left(\dfrac{4}{3}-\dfrac{3}{2}\right)^2-2:\left|-\dfrac{1}{9}\right|+\dfrac{-5}{18}\)

\(=\left(\dfrac{8}{6}-\dfrac{9}{6}\right)^2-2:\dfrac{1}{9}-\dfrac{5}{18}\)

\(=\dfrac{1}{36}-18-\dfrac{5}{18}=\dfrac{1}{36}-\dfrac{10}{36}-18=-\dfrac{9}{36}-18\)

\(=-18-\dfrac{1}{4}=-18,25\)

d: \(\left(-\dfrac{3}{4}\right)^2:\left(-\dfrac{1}{4}\right)^2+9\left(\dfrac{1}{3}\right)^2+\left|-\dfrac{3}{2}\right|\)

\(=\left(-\dfrac{3}{4}:\dfrac{-1}{4}\right)^2+9\cdot\dfrac{1}{9}+\dfrac{3}{2}\)

\(=3^2+1+\dfrac{3}{2}=9+1+\dfrac{3}{2}=10+\dfrac{3}{2}=11,5\)

Bài 4:

a: \(216x^3+27y^3=27\left(8x^3+y^3\right)\)

\(=27\left[\left(2x\right)^3+y^3\right]\)

\(=27\left(2x+y\right)\left(4x^2-2xy+y^2\right)\)

b: \(64a^3-8=8\left(8a^3-1\right)\)

\(=8\left[\left(2a\right)^3-1^3\right]\)

\(=8\left(2a-1\right)\left(4a^2+2a+1\right)\)

c: \(x^3+8=x^3+2^3=\left(x+2\right)\left(x^2-2x+4\right)\)

d: \(27x^3-8y^3=\left(3x\right)^3-\left(2y\right)^3\)

\(=\left(3x-2y\right)\left[\left(3x\right)^2+3x\cdot2y+\left(2y\right)^2\right]\)

\(=\left(3x-2y\right)\left(9x^2+6xy+4y^2\right)\)

Bài 5:

a: \(3\left(x-y\right)^2-2\left(x+y\right)^2-\left(x-y\right)\left(x+y\right)\)

\(=3\left(x^2-2xy+y^2\right)-2\left(x^2+2xy+y^2\right)-\left(x^2-y^2\right)\)

\(=3x^2-6xy+3y^2-2x^2-4xy-2y^2-x^2+y^2\)

\(=2y^2-10xy\)

b: \(\left(x-y\right)^3-3\left(x-y\right)^2\cdot x+3\left(x-y\right)\cdot x^2-x^3\)

\(=\left(x-y-x\right)^3\)

\(=\left(-y\right)^3=-y^3\)

c: \(\left(3x+3\right)^3-2\left(x+1\right)^3-\left(5x-1\right)^2\)

\(=27\left(x+1\right)^3-2\left(x+1\right)^3-\left(5x-1\right)^2\)

\(=25\left(x+1\right)^3-25x^2+10x-1\)

\(=25x^3+75x^2+75x+25-25x^2+10x-1\)

\(=25x^3+50x^2+85x+24\)

d: \(\left(-2x+3\right)^3-\left(x+1\right)^3+\left(3x-1\right)^2\)

\(=\left(-2x+3-x-1\right)\left[\left(-2x+3\right)^2+\left(-2x+3\right)\left(x+1\right)+\left(x+1\right)^2\right]+\left(3x-1\right)^2\)

\(=\left(-3x+2\right)\left(4x^2-12x+9-2x^2+x+3+x^2+2x+1\right)+\left(3x-1\right)^2\)

\(=\left(-3x+2\right)\left(3x^2-9x+13\right)+\left(3x-1\right)^2\)

\(=-9x^3+27x^2-39x+6x^2-18x+26+9x^2-6x+1\)

\(=-9x^3+42x^2-63x+27\)

\(4\dfrac{3}{8}+5\dfrac{2}{3}\)

\(=4+5+\dfrac{3}{8}+\dfrac{2}{3}\)

\(=9+\dfrac{9}{24}+\dfrac{16}{24}\)

\(=9+\dfrac{25}{24}\)

\(=10\dfrac{1}{24}\)

\(4\dfrac{3}{8}+5\dfrac{2}{3}\)

\(=\dfrac{35}{8}+\dfrac{17}{3}\)

\(=\dfrac{105}{24}+\dfrac{136}{24}\)

\(=\dfrac{241}{24}\)

\(\dfrac{1}{5}.\left(x+2\right)^2+\dfrac{1}{3}.\left(2x-2\right)^3=\dfrac{1}{5}.\left(x+2\right)^2+\dfrac{1}{3}.2^3\)

\(\Rightarrow\left(2x-2\right)^3=2^3\)

\(\Rightarrow2x-2=2\)

\(\Rightarrow2x=2+2\)

\(\Rightarrow2x=4\)

\(\Rightarrow x=4\div2\)

\(\Rightarrow x=2\)

Vậy \(x=2\)

`1/5 . (x+2)^2 + 1/3 . (2x - 2)^3 = 1/5 . (x+2)^2 + 1/3 . 2^3`

`<=> 1/5 . (x+2)^2 -  1/5 . (x+2)^2+ 1/3 . (2x - 2)^3 = 1/3 . 2^3`

`<=> 0 + 1/3 . (2x - 2)^3 = 1/3 . 2^3`

`<=> 1/3 . (2x - 2)^3 = 1/3 . 2^3`

`<=> 1/3 : 1/3 . (2x - 2)^3 = 2^3`

`<=> 1 . (2x - 2)^3 = 2^3`

`<=> (2x - 2)^3 = 2^3`

`<=> 2x - 2 = 2`

`<=> 2x = 2+2 `

`<=> 2x = 4`

`<=> x = 4 : 2`

`<=> x = 2`

Vậy `x = 2`

`A= (x+5)/(x+3 )` 

Điều kiện: `x ≠ -3`

Do `x ∈ Z => x + 5` và `x + 3∈ Z`

Để `A ∈ Z <=> x + 5 ⋮x + 3`

`<=> x + 3 + 2 ⋮ x + 3`

Do `x + 3 ⋮ x + 3`

Nên `2 ⋮ x + 3`

`=> x + 3 ∈ Ư(2) =` {`-2;-1;1;2`}

`=> x ∈` {`-5;-4;-2;-1`} (Thỏa mãn)

Vậy ...

------------------------------

`B =(x-2)/(x+1)`

Điều kiện: `x ≠ -1`

Do `x ∈ Z => x -2` và `x + 1 ∈ Z`

Để `B ∈ Z <=> x -2 ⋮x + 1`

`<=> x + 1 - 3 ⋮x + 1`

Do `x + 1 ⋮x + 1`

Nên `3⋮x + 1`

`=> x + 1 ∈ Ư(3) =` {`-3;-1;1;3`}

`=> x ∈` {`-4;-2;0;2`} (Thỏa mãn)

Vậy ...

\(A=\dfrac{x+5}{x+3}\in Z\)

\(\Rightarrow\left(x+5\right)⋮\left(x+3\right)\)

Mà \(\left(x+3\right)⋮\left(x+3\right)\)

\(\Rightarrow\left(x+5\right)-\left(x+3\right)⋮\left(x+3\right)\)

\(\Rightarrow2⋮\left(x+3\right)\)

\(\Rightarrow\left(x+3\right)\inƯ\left(2\right)\)

\(\Rightarrow\left(x+3\right)\in\left\{1;-1;-2;2\right\}\)

Ta có bảng giá trị:

Vậy \(x\in\left\{-2;-4;-1;-5\right\}\)

Những câu còn lại, cách làm tương tự, nếu như còn thắc mắc thì bạn tag mình nhé.