1.

\(2sinx+cosx=4\)

\(\Leftrightarrow\sqrt{5}\left(\dfrac{2}{\sqrt{5}}sinx+\dfrac{1}{\sqrt{5}}cosx\right)=4\)

\(\Leftrightarrow sin\left(x+arccos\dfrac{2}{\sqrt{5}}\right)=\dfrac{4}{\sqrt{5}}>1\)

\(\Rightarrow2sinx+4cosx-4\ne0\)

Khi đó: 

\(2P.sinx+P.cosx-4P=sinx-2cosx-3\)

\(\Leftrightarrow\left(2P-1\right)sinx+\left(P+2\right)cosx=4P-3\)

Phương trình có nghiệm khi:

\(\left(2P-1\right)^2+\left(P+2\right)^2\ge\left(4P-3\right)^2\)

\(\Leftrightarrow4P^2-4P+1+P^2+4P+4\ge16P^2+9-24P\)

\(\Leftrightarrow11P^2-24P+4\le0\)

\(\Leftrightarrow\dfrac{2}{11}\le P\le2\)

\(\Rightarrow maxP=2\)

1.

\(\left\{{}\begin{matrix}x_{A'}=x_A+\left(-1\right)=2\\y_{A'}=y_A+3=0\end{matrix}\right.\) \(\Rightarrow A'\left(2;0\right)\)

2.

\(\overrightarrow{MP}=\left(4;2\right)\)

\(\Rightarrow\left\{{}\begin{matrix}x_{N'}=x_N+4=-4+4=0\\y_{N'}=y_N+2=1+2=3\end{matrix}\right.\)

\(\Rightarrow N'\left(0;3\right)\)

3.

\(\overrightarrow{MM'}=\left(13;7\right)\Rightarrow\overrightarrow{v}=\overrightarrow{MM'}=\left(13;7\right)\)

4.

\(\overrightarrow{MN}=\left(-2;-1\right)\Rightarrow MN=\sqrt{\left(-2\right)^2+\left(-1\right)^2}=\sqrt{5}\)

\(\Rightarrow M'N'=MN=\sqrt{5}\)

5.

Gọi G là trọng tâm ABC \(\Rightarrow G\left(2;1\right)\)

\(\overrightarrow{BC}=\left(-6;-3\right)\)

\(\Rightarrow\left\{{}\begin{matrix}x_{G'}=2-6=-4\\y_{G'}=1-3=-2\end{matrix}\right.\) \(\Rightarrow G'\left(-4;-2\right)\)

Câu 1: \(\frac{\pi}{2}<\alpha,\beta<\pi\)

=>\(\sin\alpha>0;\sin\beta>0;cos\alpha<0;cos\beta<0\)

\(\sin^2\alpha+cos^2\alpha=1\)

=>\(cos^2\alpha=1-\sin^2\alpha=1-\left(\frac13\right)^2=\frac89\)

mà \(cos\alpha<0\)

nên \(cos\alpha=-\frac{2\sqrt2}{3}\)

Ta có: \(\sin^2\beta+cos^2\beta=1\)

=>\(\sin^2\beta=1-\left(-\frac23\right)^2=1-\frac49=\frac59\)

mà \(\sin\beta>0\)

nên \(\sin\beta=\frac{\sqrt5}{3}\)

\(\sin\left(\alpha+\beta\right)=\sin\alpha\cdot cos\beta+cos\alpha\cdot\sin\beta\)

\(=\frac13\cdot\frac{-2}{3}+\frac{-2\sqrt2}{3}\cdot\frac{\sqrt5}{3}=\frac{-\sqrt2-2\sqrt{10}}{9}\)

Câu 2:

\(P=cos\left(a+b\right)\cdot cos\left(a-b\right)\)

\(=\frac12\cdot\left\lbrack cos\left(a+b+a-b\right)+cos\left(a+b-a+b\right)\right\rbrack=\frac12\cdot\left\lbrack cos2a+cos2b\right\rbrack\)

\(=\frac12\cdot\left\lbrack2\cdot cos^2a-1+2\cdot cos^2b-1\right\rbrack=cos^2a+cos^2b-1\)

\(=\left(\frac13\right)^2+\left(\frac14\right)^2-1=\frac19+\frac{1}{16}-1=\frac{25}{144}-1=-\frac{119}{144}\)

1. Đề lỗi

2.

Đường tròn (C) tâm \(I\left(1;-1\right)\) bán kính \(R=\sqrt{1^2+\left(-1\right)^2-\left(-7\right)}=3\)

a.

\(d\left(I;D\right)=\dfrac{\left|1-1-4\right|}{\sqrt{1^2+1^2}}=2\sqrt{2}< R\)

\(\Rightarrow D\) cắt (C) tại 2 điểm phân biệt

b.

Gọi H là trung điểm MN \(\Rightarrow IH\perp MN\Rightarrow IH=d\left(I;D\right)=2\sqrt{2}\)

ÁP dụng định lý Pitago trong tam giác vuông IHM:

\(HM=\sqrt{IM^2-IH^2}=\sqrt{R^2-IH^2}=\sqrt{9-8}=1\)

\(\Rightarrow MN=2MH=2\)

\(S_{IMN}=\dfrac{1}{2}IH.MN=2\sqrt{2}\)

3.

Đường tròn (C) tâm \(I\left(2;3\right)\) bán kính \(R=\sqrt{2}\)

Đường còn (C') tâm \(I'\left(1;2\right)\) bán kính \(R'=2\sqrt{2}\)

Gọi tiếp tuyến chung của (C) và (C') là (d) có pt: \(ax+by+c=0\) với \(a^2+b^2\ne0\)

\(\Rightarrow\left\{{}\begin{matrix}d\left(I;\left(d\right)\right)=R\\d\left(I';\left(d\right)\right)=R'\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}\dfrac{\left|2a+3b+c\right|}{\sqrt{a^2+b^2}}=\sqrt{2}\left(1\right)\\\dfrac{\left|a+2b+c\right|}{\sqrt{a^2+b^2}}=2\sqrt{2}\end{matrix}\right.\)

\(\Rightarrow\left|a+2b+c\right|=2\left|2a+3b+c\right|\)

\(\Rightarrow\left[{}\begin{matrix}4a+6b+2c=a+2b+c\\4a+6b+2c=-a-2b-c\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}3a+4b+c=0\\5a+8b+3c=0\end{matrix}\right.\) \(\Rightarrow\left[{}\begin{matrix}c=-3a-4b\\c=-\dfrac{5a+8b}{3}\end{matrix}\right.\)

Thế vào (1):

\(\Rightarrow\left[{}\begin{matrix}\dfrac{\left|2a+3b-3a-4b\right|}{\sqrt{a^2+b^2}}=\sqrt{2}\\\dfrac{\left|2a+3b-\dfrac{5a+8b}{3}\right|}{\sqrt{a^2+b^2}}=\sqrt{2}\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}\left|a+b\right|=\sqrt{2\left(a^2+b^2\right)}\\\left|a+b\right|=3\sqrt{2\left(a^2+b^2\right)}\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}a^2+2ab+b^2=2a^2+2b^2\\a^2+2ab+b^2=18a^2+18b^2\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}\left(a-b\right)^2=0\\17a^2-2ab+17b^2=0\left(vn\right)\end{matrix}\right.\)

\(\Rightarrow a=b\) \(\Rightarrow c=-3a-4b=-7a\)

Thế vào pt (d):

\(ax+ay-7a=0\Leftrightarrow x+y-7=0\)

4.

ĐKXĐ: \(x\ge-\dfrac{3}{2}\)

\(4\left(x+1\right)^2< \left(x+10\right)\left(1-\sqrt{3+2x}\right)^2\)

\(\Leftrightarrow4\left(x+1\right)^2< \left(x+10\right)\left(\dfrac{-2-2x}{1+\sqrt{3+2x}}\right)^2\)

\(\Leftrightarrow4\left(x+1\right)^2< \dfrac{\left(x+10\right)4\left(x+1\right)^2}{\left(1+\sqrt{3+2x}\right)^2}\)

\(\Leftrightarrow\left\{{}\begin{matrix}x\ne-1\\\dfrac{x+10}{\left(1+\sqrt{3+2x}\right)^2}>1\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x\ne-1\\x+10>1+3+2x+2\sqrt{3+2x}\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x\ne-1\\6-x>2\sqrt{3+2x}\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x\ne-1\\6-x>0\\\left(6-x\right)^2>4\left(3+2x\right)\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x\ne-1\\x< 6\\x^2-20x+24>0\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}x\ne-1\\x< 10-2\sqrt{19}\end{matrix}\right.\)

Kết hợp ĐKXĐ ta được nghiệm của BPT là: 

\(\left[{}\begin{matrix}-\dfrac{3}{2}\le x< -1\\-1< x< 10-2\sqrt{19}\end{matrix}\right.\)