`a,`

Vì `a` và `b` là `2` đại lượng tỉ lệ thuận

`\rightarrow a=k*b`

Thay `a=3, b=33`

`\rightarrow 3=k*33`

`\rightarrow k=3 \div 33`

`\rughtarrow k=`\(\dfrac{1}{11}\)

Vậy, hệ số tỉ lệ `k=`\(\dfrac{1}{11}\)

`b,`

Khi `b=-7 \rightarrow a=`\(\dfrac{1}{11}\cdot-7=-\dfrac{7}{11}\)

`,`

Khi `a=110 \rightarrow b= 110 \div`\(\dfrac{1}{11}\)`= 1210`

Lời giải:

a. Gọi $k$ là hệ số tỉ lệ của $a$ đối với $b$. Ta có: $a=bk$

$\Rightarrow k=\frac{a}{b}=\frac{3}{33}=\frac{1}{11}$

b. Ta có: $a=\frac{b}{11}$
Khi $b=-7$ thì $a=\frac{b}{11}=\frac{-7}{11}$

c. $110=a=\frac{b}{11}\Rightarrow b=110.11=1210$

a,A= -a-b+c+a+b+c=2c

b, khi a=1,b=-1,c=-2 thì 

A=2(-2)=-4

a)

\(A=\left(-a-b+c\right)-\left(-a-b-c\right)\)

\(A=-a-b+c-\left(-a\right)+b+c\)

\(A=-a+\left(-b\right)+c+a+b+c\)

\(A=\left[\left(-a\right)+a\right]+\left[\left(-b\right)+b\right]+\left(c+c\right)\)

\(A=0+0+2c\)

\(A=2c\)

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b)

Cách 1 :  \(A=\left(-1-\left(-1\right)+\left(-2\right)\right)-\left(1-\left(-1\right)-\left(-2\right)\right)\)

\(A=-1-\left(-1\right)+\left(-2\right)-\left(-1\right)+\left(-1\right)+\left(-2\right)\)

\(A=-1+1+\left(-2\right)+1+\left(-1\right)+\left(-2\right)\)

\(A=\left[\left(-1\right)+1+1+\left(-1\right)\right]+\left[\left(-2\right)+\left(-2\right)\right]\)

\(A=0+\left(-4\right)=\left(-4\right)\)

Cách 2 : Từ ý   a   suy ra :

\(A=\left(-2\right)\cdot2=\left(-4\right)\)

\(A=16-2\cdot\left(-12\right)=40\)

\(a^2+b^2=\left(a^2+2ab+b^2\right)-2ab=\left(a+b\right)^2-2ab=\left(-4\right)^2-2\left(-12\right)=16+24=40\)

\(a,A=\left(x-1\right)\left(x+2\right)\left(x+3\right)\left(x+6\right)-2018\)

\(=\left(x^2+5x-6\right)\left(x^2+5x+6\right)-2018\)

Đặt \(x^2+5x=a\)

\(\Rightarrow A=\left(a-6\right)\left(a+6\right)-2018=a^2-2054\)

\(\Rightarrow A_{min}=2054\Leftrightarrow a=0\)

\(\Rightarrow x^2+5x=0\Leftrightarrow x\left(x+5\right)=0\)

\(\Leftrightarrow x\in\left\{0;-5\right\}\)

\(b,B=\left(x-1\right)\left(x-4\right)\left(x-5\right)\left(x-8\right)+2018.\)

\(=\left(x^2-9x+8\right)\left(x^2-9x+20\right)+2018\)

Đặt \(x^2-9x+14=a\)

\(\Rightarrow B=\left(a-6\right)\left(a+6\right)+2018\)

\(=a^2-36+2018=a^2+1982\)

\(\Rightarrow B_{min}=1982\Leftrightarrow a^2=0\Rightarrow a=0\)

\(\Rightarrow x^2-9x+14=0\)

\(\Rightarrow x^2-2x-7x+14=0\)

\(\Leftrightarrow x\left(x-2\right)-7\left(x-2\right)=0\)

\(\Rightarrow\left(x-2\right)\left(x-7\right)=0\)

\(\Rightarrow x\in\left\{2;7\right\}\)

a: \(P=-5\sqrt{\dfrac{160}{90}}=-5\cdot\dfrac{4}{3}=-\dfrac{20}{3}\)

b: \(Q=\sqrt{a}-\sqrt{b}+2\sqrt{b}=\sqrt{a}+\sqrt{b}\)