Giải:

tam giác ABC có: \(\widehat{A}+\widehat{B}+\widehat{C}=180^o\)

=> \(\widehat{B}+\widehat{C}=180^o-\widehat{A}=180^o-72^o=108^o\)

Tam giác IBC có: \(\widehat{BIC}+\widehat{B_1}+\widehat{C_1}=180^o\)

=> \(\widehat{BIC}=180^o-\left(\widehat{B_1}+\widehat{C_1}\right)\)

= \(180^o-\left(\dfrac{1}{2}\widehat{B}+\dfrac{1}{2}\widehat{C}\right)=180^o-\dfrac{1}{2}\left(\widehat{B}+\widehat{C}\right)\)

\(=180^o-\dfrac{1}{2}\cdot108^o=180^o-54^o=126^o\)

Câu 2:

Ta có: 3n +8 chia hết cho n + 2 (1)

Mà: n+2 chia hết cho n + 2

=>3(n+2) chia hết cho n + 2

=>3n+6 chia hết cho n + 2 (2)

Từ (1) và (2) =>(3n+8)-(3n+6) chia hết cho n + 2

=>2  chia hết cho n + 2

=>n+2 thuộc Ư(2)

=> n+2thuộc {1;2}⇒n+2∈{1;2}

⇒n∈{0}

Vậy n=0

Tick cho mình đi !

x=4

x^2=4

2^2=4

4=4

**** nha avatar của bạn đẹp quá

\(\left(x+2\right)\left(x+4\right)\left(x^2-9\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}x+2=0\\x+4=0\\x^2-9=0\Rightarrow x^2=9\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=-2\\x=-4\\\left[{}\begin{matrix}x=3\\x=-3\end{matrix}\right.\end{matrix}\right.\)

Vậy................

\(\left(5x-2\right)^{20}=\left(5x-2\right)^{16}\)

\(\Leftrightarrow\left(5x-2\right)^{20}-\left(5x-2\right)^{16}=0\)

\(\Leftrightarrow\left(5x-2\right)^{16}\left[\left(5x-2\right)^4-1\right]=0\)

\(\Leftrightarrow\left[{}\begin{matrix}\left(5x-2\right)^{16}=0\\\left(5x-2\right)^4-1=0\Rightarrow\left(5x-2\right)^4=1\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}5x-2=0\\\left[{}\begin{matrix}5x-2=1\\5x-2=-1\end{matrix}\right.\end{matrix}\right.\)

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

Vậy..................

Số bi của Bình Là:

        30 : 3 - 3 = 7 (viên)

                  Đ/S: 7 viên bi

Ta có: 9 : 2 0 = 0,45 = 45%

Để \(\dfrac{6}{\sqrt{x}}\in Z\) <=> \(\sqrt{x}\inƯ\left(6\right)\)

mà \(\sqrt{x}\ge0\)

=> \(\sqrt{x}\in\left\{1;2;3;6\right\}\)

\(\Rightarrow x\in\left\{1;4;9;36\right\}\)

Vậy..............

1,2075km=1207,5m

0,452 hm=45,2 m

12,075 km=12075m

10,241 dam=102,41 m

ca 3 so kho chua so gao la :

[ 34,9 + 31,7 + 33,8 ] : 2 = 50,2 [ tan ]

kho thu 1 co so gao la :

50,2 - 31,7 = 18,5 [ tan ]

kho thu 2 co so gao la :

50,2 - 33,8 = 16,4 [ tan ]

kho thu 3 co so gao la 

50,2 - 34,9 = 15,3 [ tan ]

tick cho minh nha