\(x\cdot12,25-x+x\cdot2,75=1050\)

\(\Rightarrow x\cdot12,25-x\cdot1+x\cdot2,75=1050\)

\(\Rightarrow x\left(12,25-1+2,75\right)=1050\)

\(\Rightarrow x\cdot14=1050\)

\(\Rightarrow x=\frac{1050}{14}=75\)

dau . la dau j vay ban

a) <=> 15-5x-20=-12-3

<=> -5x=-12-3-15+20=-10

=>x=-10:(-5)=2

b)<=>7-x-25-7=-25

<=> -x=-25-7+25+7=0 =>x=0

c) /x+2/=0 => x+2=0 =>x=-2

d) sai đề

e)<=> /x-5/ = 7

<=> \(\orbr{\begin{cases}x-5=7\\x-5=-7\end{cases}}\)

<=> \(\orbr{\begin{cases}x=12\\x=-2\end{cases}}\)

g) <=> -x-20-8+2x=-15

<=> x=-15+20+8=13

d là | x + 3 | = 7 - ( - 2 )

\(\frac{x}{3}=\frac{3}{x}\)

\(\Leftrightarrow9=x^2\)

\(\Leftrightarrow x=\sqrt{9}\)

\(\Leftrightarrow x\in\left\{-3;3\right\}\)

\(\frac{8}{5}=\frac{-12}{x}\)

\(\Leftrightarrow8x=-60\)

\(\Leftrightarrow x=\frac{-15}{2}\)

\(\frac{x}{-4}=\frac{-4}{x}\)

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

\(\Leftrightarrow x^2=16\)

\(\Leftrightarrow x=\sqrt{16}\)

\(\Leftrightarrow x\in\left\{-4;4\right\}\)

câu 1 : x = 3

vì 3/3 cũng = 3/3

- 12 . ( x - 5 ) + 7 . ( 3 - x ) = 5

=> - 12x - 12 . 5 + 7 . 3 - 7x = 5

=> - 12x - 60 + 21 - 7x = 5

=> ( - 12 - 7 )x + ( 60 + 21 ) = 5

=> - 19x + 81 = 5

=> - 19x = - 76

=> x = 4

30 . ( x + 2 ) - 6 . ( x + 5 ) - 24x = 100

=> 30x + 30 . 2 - 6x + 6 . 5 - 24x = 100

=> 30x + 60 - 6x + 30 - 24x = 100

=> 0 . x = 100

=> Không có giá trị x

( x + 1 ) + ( x + 2 ) + . . . + ( x + 99 ) = 0

=> x . 99 + ( 1 + 2 + . . . + 99 ) = 0

=> x . 99 + 4950 = 0

=> x . 99 = - 4950

=> x = - 50

\(\left(x+1\right)+\left(x+2\right)+...+\left(x+99\right)=0\)

\(x+1+x+2+...+x+99=0\)

\(99x+\left(1+2+3+...+98+99\right)=0\)

 \(99x+\frac{\left(99+1\right).99}{2}=0\)

\(99x+4950=0\)

\(99x=-4950\)

\(x=-4950:99=-50\)

99 - 3(x + 17) = 45

=> 3(x + 17) = 99 - 45

=> 3x + 51 = 54

=> 3x = 54 - 53

=> 3x = 3

=> x = 3 : 3

=> x = 1

vậy_

a,99-3x-51=45

3x=45+51-99

3x=-3

x=-1

b,x⁵:8=4

x⁵=32

x=2

c,3.x³=375

x³=125

x=5

d,12.x-33=3⁵

12x=276

x=23

e,4x⁵=128

x⁵=32

x=2

g,2^x:4=16

2^x=64

x=6

a) \(\frac{45-\left(3x+9\right)}{13}=42\)

\(\Leftrightarrow45-\left(3x+9\right)=546\)

\(\Leftrightarrow3x+9=-501\)

\(\Leftrightarrow3x=-510\)

\(\Leftrightarrow x=-170\)

b) \(\left(x+1\right)+\left(2x+2\right)+...+\left(20x+20\right)=1050\)

\(\Leftrightarrow x+1+2x+2+...+20x+20=1050\)

\(\Leftrightarrow\left(x+1\right)+2\left(x+1\right)+....+20\left(x+1\right)=1050\)

\(\Leftrightarrow\left(x+1\right)\left(1+2+3+...+20\right)=1050\)

\(\Leftrightarrow\left(x+1\right)\left[\frac{\left(20+1\right).20}{2}\right]=1050\)

\(\Leftrightarrow\left(x+1\right).210=1050\)

\(\Leftrightarrow x+1=5\)

\(\Leftrightarrow x=4\)

a)15/8+3/4-5/12

=45+18-10/24

=53/24

b)11/24.12/33+5/6

=11.12/12.2.11.3+5/6

=1/6+5/6

=6/6=1

c)15/8+7/24:5/8

=15/8+7/24.8/5

=15/8+7.8/3.8.5

=15/8+7/15

=đề sai, nếu đúng thì như này

=8/15+7/15

=15/15=1

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