a: ĐKXĐ: a∉{-1/3;-3}

\(\frac{3a-1}{3a+1}+\frac{a-3}{a+3}=2\)

=>\(\frac{\left(3a-1\right)\left(a+3\right)+\left(3a+1\right)\left(a-3\right)}{\left(3a+1\right)\left(a+3\right)}=2\)

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

=>\(2\left(3a^2+9a+a+3\right)=3a^2+9a-a-3+3a^2-9a+a-3\)

=>\(6a^2+20a+6=6a^2-6\)

=>20a=-12

=>a=-3/5(nhận)

b: ĐKXĐ: a∉{5/2;2/3}

\(\frac{2a-9}{2a-5}+\frac{3a}{3a-2}=2\)

=>\(\frac{2a-5-4}{2a-5}+\frac{3a-2+2}{3a-2}=2\)

=>\(1-\frac{4}{2a-5}+1+\frac{2}{3a-2}=2\)

=>\(\frac{2}{3a-2}=\frac{4}{2a-5}\)

=>\(\frac{4}{6a-4}=\frac{4}{2a-5}\)

=>6a-4=2a-5

=>4a=-1

=>a=-1/4(nhận)

c: ĐKXĐ: a<>-3

\(\frac{10}{3}-\frac{3a-1}{4a+12}-\frac{7a+2}{6a+18}=2\)

=>\(\frac{3a-1}{4a+12}+\frac{7a+2}{6a+18}=\frac{10}{3}-2=\frac43\)

=>\(\frac{3\left(3a-1\right)}{12\left(a+3\right)}+\frac{2\left(7a+2\right)}{12\left(a+3\right)}=\frac43\)

=>\(\frac{9a-3+14a+4}{12\left(a+3\right)}=\frac{4\cdot4\cdot\left(a+3\right)}{12\left(a+3\right)}\)

=>23a+1=16(a+3)=16a+48

=>7a=47

=>a=47/7(nhận)

Ta có:\(-3a-\left\{-\left(-4a+5\right)+\left[-\left(5-6a\right)+\left(-12-4a\right)\right]\right\}\)

\(=-3a-\left[4a-5+\left(6a-5-12-4a\right)\right]\)

\(=-3a-\left(4a-5+6a-5-12-4a\right)\)

\(=-3a-\left(6a-22\right)=-3a-6a+22=-9a+22\)

Chúc bạn học tốt

1: C=4a+2a+10b-b

=6a+9b

=3(2a+3b)

=3*12=36

D=21a+9b-6a-4b

=15a+5b

=5(3a+b)

=5*18=90

B=5a+7a-4b-8b

=12a-12b

=12(a-b)

=12*8=96

4:

Gọi hai số cần tìm là a,b

Theo đề, ta có hệ phương trình:

a+b=38570 và a=3b+922

=>a=29158 và b=9412

1: C=4a+2a+10b-b

=6a+9b

=3(2a+3b)

=3*12=36

D=21a+9b-6a-4b

=15a+5b

=5(3a+b)

=5*18=90

B=5a+7a-4b-8b

=12a-12b

=12(a-b)

=12*8=96

Câu 5:

\(D\left(2\right)=21a+9b-6a-4b\)

\(D\left(2\right)=\left(21a-6a\right)+\left(9b-4b\right)\)

\(D\left(2\right)=15a+5b\)

Mà: \(3a+b=18\Rightarrow b=18-3b\)

\(\Rightarrow D\left(2\right)=15a+5\left(18-3b\right)\)

\(D\left(2\right)=15a+90-15a\)

\(D\left(2\right)=90\)

Vậy: ...

Câu 4:

\(D\left(1\right)=4a+10b-b+2a\)

\(D\left(1\right)=\left(4a+2a\right)+\left(10b-b\right)\)

\(D\left(1\right)=6a+9b\)

Mà: \(2a+3b=12\Rightarrow a=\dfrac{12-3b}{2}\)

\(\Rightarrow D\left(1\right)=6\left(\dfrac{12-3b}{2}\right)+9b\)

\(D\left(1\right)=\dfrac{6\left(12-3b\right)}{2}+9b\)

\(D\left(1\right)=3\left(12-3b\right)+9b\)

\(D\left(1\right)=36-9b+9b\)

\(D\left(1\right)=36\)

Vậy: ...

4:

D=6a+9b=3(2a+3b)=36

5: 

D=15a+5b=5(3a+b)=90

Câu 5:
D=21a+9b-6a-4b

=21a-6a+9b-4b

=15a+5b

=5(3a+b)

\(=5\cdot18=90\)

Câu 4: D=4a+10b-b+2a

=4a+2a+10b-b

=6a+9b

=3(2a+3b)

\(=3\cdot12=36\)

Câu 3:

C=5a-4b+7a+8

=5a+7a-4b+8

=12a-12b+8b+8

=12(a-b)+8b+8

=8(a-b)+8b+8

=8a-8b+8b+8

=8a+8