\(\left|\overrightarrow{a}\right|=\sqrt{\left(4\right)^2+\left(-m\right)^2}\)

\(\Leftrightarrow\sqrt{20}=\sqrt{16+m^2}\)

\(\Leftrightarrow4=m^2\)

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

Vậy...

Bài 25:

Để \(\frac{3x+8}{x+1}\) là số nguyên thì 3x+8⋮x+1

=>3x+3+5⋮x+1

=>5⋮x+1

=>x+1∈{1;-1;5;-5}

=>x∈{0;-2;4;-6}

=>A={0;-2;4;-6}

|x+2|<5

mà x là số tự nhiên

nên x∈{0;1;2}

=>B={0;1;2}

A={0;-2;4;-6}; B={0;1;2}

A\(\cap\) B={0;-2;4;-6}\(\cap\) {0;1;2}

={0}

A\(\cup\) B={0;-2;4;-6}\(\cup\) {0;1;2}

={0;-2;4;-6;1;2}

A\B={0;-2;4;-6}\{0;1;2}

={-2;4;-6}

B\A={0;1;2}\{0;-2;4;-6}

={1;2}

Có đáp số 6(mJ) ko bạn?

Chọn A.

\(2sin^2x-cosx+1=0\Rightarrow2\cdot\dfrac{1-cos2x}{2}-cosx+1=0\)

\(\Rightarrow1-\left(2cos^2x-1\right)-cosx+1=0\)

\(\Rightarrow-2cos^2x-cosx+3=0\)

\(\Rightarrow\left[{}\begin{matrix}cosx=1\\cosx=-\dfrac{3}{2}\left(loại\right)\end{matrix}\right.\)\(\Rightarrow x=k2\pi\)

bn làm đr

đúng rùi

Câu 23: C

Câu 24: C

Anh ơi. Nhưng e đang cần câu 25 cơ ạ

25 Because this TV programme is boring, I don't like it

26 They started playing basketball in 2010

because thí TV programme is boring, I do not like it