a) 90/x - 36/x-6 = 2.

ĐKXĐ: x≠0, x≠6.

<=> 90(x-6)-36x-2x(x-6)=0

<=> 90x-540-36x-2x²+12x=0

<=> -2x²+66x-540=0

<=> \(\left[{}\begin{matrix}x=18\left(tm\right)\\x=15\left(tm\right)\end{matrix}\right.\)

b) 1/x+1/x+10=1/12

ĐKXĐ: x≠0

<=> 1/x+1/x+10-1/12=0

<=> 12+12+10.12x-x=0

<=> 12+12+120x-x=0

<=> 119x+24=0

<=> 119x=-24

<=> x= -24/119(tm)

a, \(\frac{5}{x+7}+\frac{8}{2x+14}=\frac{3}{2}\) Đkxđ : \(x\ne-7\)

⇔ \(\frac{5}{x+7}+\frac{8}{2\left(x+7\right)}=\frac{3}{2}\)

⇔ \(\frac{10}{2\left(x+7\right)}+\frac{8}{2\left(x+7\right)}=\frac{3\left(x+7\right)}{2\left(x+7\right)}\)

⇒ \(10+8=3\left(x+7\right)\)

⇔ \(10+8=3x+21\)

⇔ \(-3x=21-10-8\)

⇔ \(-3x=3\)

⇔ \(x=-1\) ( tm )

Ptr có tập nhiệm : S \(=\left\{-1\right\}\)

b, \(\frac{x+3}{x-3}-\frac{1}{x}=\frac{3}{x\left(x-3\right)}\) Đkxđ : \(x\ne3;x\ne0\)

⇔ \(\frac{x\left(x+3\right)}{x\left(x-3\right)}-\frac{1\left(x-3\right)}{x\left(x-3\right)}=\frac{3}{x\left(x-3\right)}\)

⇒ \(x\left(x-3\right)-1\left(x-3\right)=3\)

⇔ \(x^2-3x-x+3=3\)

⇔ \(x^2-4x=0\)

⇔ \(x\left(x-4\right)=0\)

⇔ \(\left\{{}\begin{matrix}x=0\\x-4=0\end{matrix}\right.\)

⇔\(\left\{{}\begin{matrix}x=0\left(ktm\right)\\x=4\left(tm\right)\end{matrix}\right.\)

Ptr có tập nhiệm : S \(=\left\{4\right\}\)

a)ĐKXĐ:x\(\ne\)0 x\(\ne\)6

=>90(x-6)-36x=2x(x-6)

<=>90x-540-36x=2x²-12x

<=>2x²-12x=54x-540

<=>2x²-66x+540=0

<=>x²-33x+270=0

<=>(x²-15x)-(18x-270)=0

<=>(x-15)(x-18)=0

<=>x=15(tm) hoặc x=18(tm)

b)ĐKXĐ:x\(\ne\)0 x\(\ne\)3

sai đề

c)ĐKXĐ:x\(\ne\)-2 x\(\ne\)2

=>3(x-2)-2(x+2)+8=0

<=>3x-6-2x-4+8=0

<=>x-2=0

<=>x=2(L)

Vậy PT vô nghiệm

d)ĐKXĐ: x\(\ne\)-7

=>10+8=\(\dfrac{3}{2}\)(câu này hình như đề cũng sai)

Bài 1 : Tìm x

a, 18 . x = -90

x=-90 : 18

x= -5

b, ( -3 ) . ( x +12 ) = -36

x+12= -36 : (-3)

x+12= 12

x= 0

c, 2x - 13 = -37

2x = -37+13

2x=-24

x=-24 : 2

x=-12

d, ( 25 - x ) . 12 = - 24

25 - x = -24 : 12

25 -x = -2

x= 25+2

x=27

a/ \(18.x=-90\Leftrightarrow x=-\frac{90}{18}=-5\)

b/ \(\left(-3\right)\left(x+12\right)=-36\Leftrightarrow x+12=12\Leftrightarrow x=0\)

c/ \(2x-13=-37\Leftrightarrow2x=-24\Leftrightarrow x=-12\)

d/ \(\left(25-x\right)12=-24\Leftrightarrow25-x=2\Leftrightarrow x=23\)

KL: .....................

1 : Tìm x

a, 18 . x = -90

            x=-90 : 18

            x= -5

b, ( -3 ) . ( x +12 ) = -36

                     x+12= -36 : (-3)

                     x+12= 12

                           x= 0

c, 2x - 13 = -37

           2x = -37+13

           2x = -24

             x = -24 : 2

            x  = -12

d, ( 25 - x ) . 12 = - 24

               25 - x = -24 : 12

                 25 - x = -2

                       x = 25 + 2

                       x = 27

b) \(\frac{x-90}{10}+\frac{x-76}{12}+\frac{x-58}{14}+\frac{x-36}{16}+\frac{x-15}{17}=15\)

=> \(\left(\frac{x-90}{10}-1\right)+\left(\frac{x-76}{12}-2\right)+\left(\frac{x-58}{14}-3\right)+\left(\frac{x-36}{16}-4\right)+\left(\frac{x-15}{17}-5\right)=0\)

=> \(\frac{x-100}{10}+\frac{x-100}{12}+\frac{x-100}{14}+\frac{x-100}{16}+\frac{x-100}{17}=0\)

=> \(\left(x-100\right)\left(\frac{1}{10}+\frac{1}{12}+\frac{1}{14}+\frac{1}{16}+\frac{1}{17}\right)=0\)

Vì \(\frac{1}{10}+\frac{1}{12}+\frac{1}{14}+\frac{1}{16}+\frac{1}{17}\ne0\)

=> x - 100 = 0

=> x = 100

a 

x=1000:10

x=100

b 

x=72:36

x=2

c

x+10=90

x=90-10

x=80

a) \(x\times10=1000\)
\(\Rightarrow x=1000:10\)
\(\Rightarrow x=100\)
b) \(x\times36=72\)
\(\Rightarrow x=72:36\)
\(\Rightarrow x=2\)
c) \(x+3+7=90\)
\(\Rightarrow x+10=90\)
\(\Rightarrow x=90-10\)
\(\Rightarrow x=80\)

a. X x 10 = 1000

    x          = 1000 : 10 

    x           =  100

b. X x 36 = 72

    x          = 72 : 36 

     x           =  2

c. X+3+7=90

    x + 3   = 90- 7

    x + 3   =  83

    x         = 83 - 3

    x          = 80

   41 x 36 + 59 x 90 + 41 x 84 + 59 x 30

= 41 x (36 + 84) + 59 x (90 + 30)

= 41 x 120 + 59 x 120

= 120 x (41 + 59)
= 120 x 100

= 12000

   41 x 36 + 59 x 90 + 41 x 84  + 59 x 30

= 41 x ( 36 + 84 ) + 59 x ( 90 + 30 )

= 41 x 120 + 59 x 120

= 120 x ( 41 + 59 )

= 120 x 100

= 12 000

41 x 36 + 59 x 90 + 41 x 84 + 59 x 30 = 41 x 36 + 41 x 84 + 59 x 90 + 59 x 30  

                                                            = 41 x (36+84) + 59 x (90+30)

                                                            = 41 x 120 + 59 x 120                                                                 

                                                            = 120 x ( 41+59)  

                                                            = 120 x 100  

                                                            =12000