13,5×142+4,5×78×3+1,5×80×9

=13,5×142+4,5×3×78+1,5×9×80

=13,5×142+13,5×78+13,5×80

=13,5×(142+78+80)

=13,5×300

=13,5×100×3

=1350×3

=4050

X + 4,5 x X + 3 x X + 1,5 x X = 13,5

X + 4,5 x X + 3 x X + 1,5 x X + 1 = 13,5

X x ( 4,5 + 3 +1,5 + 1 ) = 13,5

X x 10  = 13,5

X = 13,5 : 10

X = 1,35

x+4,5.x+3.x+1,5.x=13,5

=> x.(1+4,5+3+1,5)=13,5

=> x.10                 =13,5

=> x                     =13,5:10

=> x                     ==1,35

Vậy x=1,35

X + 4,5 x X +3 x X +1,5 x X = 13,5

(X x 3) +4,5 + 3+ 1,5 = 13,5

X=(13,5 - 4,5 -3 -1,5) / 3

X=4,5 /3

X =1,5

Vậy X = 4,5

Ta có: \(\frac{36}{x+6}+\frac{36}{x-6}=\frac{9}{2}\)

ĐKXĐ: \(\left\{\begin{matrix}x\ne-6\\x\ne6\end{matrix}\right.\)

\(\Leftrightarrow36\left(\frac{1}{x+6}+\frac{1}{x-6}\right)=\frac{9}{2}\)

\(\Leftrightarrow36\left(\frac{x-6+x+6}{\left(x+6\right)\left(x-6\right)}\right)=\frac{9}{2}\)

\(\Leftrightarrow36.\frac{2x}{x^2-36}=\frac{9}{2}\)

\(\Leftrightarrow\frac{72x}{x^2-36}=\frac{9}{2}\)

\(\Leftrightarrow72x.2=9.\left(x^2-36\right)\)

\(\Leftrightarrow8x.2=x^2-36\) ( chia cả hai vế cho 9 )

\(\Leftrightarrow16x=x^2-36\)

\(\Leftrightarrow16x-x^2+36=0\)

\(\Leftrightarrow-x^2+16x+36=0\)

\(\Leftrightarrow x^2-16x-36=0\)

\(\Leftrightarrow x^2+2x-18x-36=0\)

\(\Leftrightarrow x\left(x+2\right)-18\left(x+2\right)=0\)

\(\Leftrightarrow\left(x+2\right)\left(x-18\right)=0\)

\(\Leftrightarrow\left[\begin{matrix}x+2=0\\x-18=0\end{matrix}\right.\Leftrightarrow\left[\begin{matrix}x=-2\\x=18\end{matrix}\right.\)

Vậy: \(x=-2;18\)

\(\frac{36}{x+6}+\frac{36}{x-6}=4,5\left(đkxđ:x\ne\pm6\right)\)

\(\Leftrightarrow\frac{36\left(x-6\right)+36\left(x+6\right)}{\left(x-6\right)\left(x+6\right)}=\frac{4,5\left(x-6\right)\left(x+6\right)}{\left(x-6\right)\left(x+6\right)}\)

\(\Leftrightarrow\frac{36\left(x-6+x+6\right)}{\left(x-6\right)\left(x+6\right)}=\frac{4,5\left(x^2-36\right)}{\left(x-6\right)\left(x+6\right)}\)

\(\Rightarrow36\times2x=4,5\left(x^2-36\right)\)

\(\Leftrightarrow72x=4,5x^2-162\)

\(\Leftrightarrow4,5x^2-72x-162=0\)

\(\Leftrightarrow4,5x^2+9x-81x-162=0\)

\(\Leftrightarrow4,5x\left(x+2\right)-81\left(x+2\right)=0\)

\(\Leftrightarrow\left(4,5x-81\right)\left(x+2\right)=0\)

\(\Leftrightarrow\left[\begin{matrix}4,5x-81=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left[\begin{matrix}x=18\\x=-2\end{matrix}\right.\left(TMĐKXĐ\right)\)

x = -2 nha cậu

\(\dfrac{-4}{x}=\dfrac{x}{-49}\\ \Rightarrow x^2=\left(-4\right)\left(-49\right)\\ \Rightarrow x^2=196\\ \Rightarrow x=\pm14\)

\(\dfrac{3.6}{x-3}=\dfrac{5}{3}\\ \Rightarrow5\left(x-3\right)=3.3.6\\ \Rightarrow5\left(x-3\right)=54\\ \Rightarrow x-3=\dfrac{54}{5}\\ \Rightarrow x=\dfrac{54}{5}+3\\ \Rightarrow x=\dfrac{69}{15}\)

\(\left(2x+1\right):2=12:3\\ \left(2x+1\right):2=4\\2x+1=2\\ 2x=1\\ x=\dfrac{1}{2} \)

\(\left(2x-14\right):3=12:9\\ \left(2x-14\right):3=\dfrac{4}{3}\\ 2x-14=4\\ 2x=16\\ x=8\)

                                                                     Bài giải

a, \(1075\cdot\left(x-3\right)\cdot\left(x-1\right)=0\)

\(\left(x-3\right)\left(x-1\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x-3=0\\x-1=0\end{cases}}\)\(\Rightarrow\orbr{\begin{cases}x=3\\x=1\end{cases}}\)

\(\Rightarrow\text{ }x\in\left\{3\text{ ; }1\right\}\)

b, \(2\cdot\left(x-7\right)+3\cdot\left(x+1\right)\)

\(=2x-14+3x+3\)

\(=5x-11\)

c, \(x+1+x+2+...+x+100=5750\)

\(\left(x+x+...+x\right)+\left(1+2+...+100\right)=5750\)

\(100x+\left(100-1+1\right)\cdot\left(100+1\right)\text{ : }2=5750\)

\(100x+100\cdot101\text{ : }5=5750\)

\(100x+50\cdot101=5750\)

\(100x+5050=5750\)

\(100x=5750-5050\)

\(100x=700\)

\(x=700\text{ : }100\)

\(x=7\)

39x[250+87]+64x[240+97]

=39x337+64x337

=(39+64)x337

=103x337

=34711

78x31+78x24+78x17-22x72

=78x(31+24+17)-22x72

=78x72-22x72

=(78-22)x72

=56x72

=4032

bn tính lại nha

39 x [ 250 + 87 ] + 64 x [ 240 + 97 ]

= 39 x 337 + 64 x 337

= 337 x ( 39 + 64 )

= 337 x 103

= 34711

bai tiep

78 x 31 + 78 x 24 +78  x  17 - 22 

= 78 x  ( 31 + 24 + 17 ) - 22 x 72

= 78 x  72 - 22 x 72

=72 x  ( 72 - 22 )

= 72 x 50

= 3600

    75%x + x = 1,5

=>  3/4x + x = 1,5

=>  7/4x       = 1,5

=>       x       = 1,5 : 7/4

=>       x       = 6/7

x(75%+1)=1,5

x1,75=1,5

x=1,5/1,75

75%×X+X=1,5

75%×X+X×1=1,5

X×(75%+1)=1,5

X×(3/4+1)=3/2

X×7/4=3/2

X=3/2÷7/4

X=3/2×4/7

X=6/7

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