a: =>2x=x+100

=>x=100

b: Trường hợp 1: x>=0

=>12x-250=x+100

=>11x=350

hay x=350/11(nhận)

Trường hợp 2: x<0

=>-12x-250=x+100

=>-13x=350

hay x=-350/13(nhận)

c: \(\Leftrightarrow x^2=200000\)

hay \(x\in\left\{200\sqrt{5};-200\sqrt{5}\right\}\)

\(x\times3,5-x\times2=30\)
\(x\times\left(3,5-2\right)=30\)
\(x\times1,5=30\)
\(x=30:1,5\)
\(x=20\)

\(3,5\times x-2\times x=30\\ \Leftrightarrow x\left(3,5-2\right)-30\\ \Leftrightarrow1,5x=30\\ \Leftrightarrow x=30:1,5\\ \Leftrightarrow x=20\)

Vậy \(x=20\)

X x 3,5 - X x 2 = 30

X x (3.5 - 2)    = 30

X x 1.5            = 30

X                     = 30 : 1.5

X                     = 20

\(x⋮\) 5; \(x\) ⋮ 9; \(x\) ≤ 400

\(x\) ⋮ 5; 9 ⇒ \(x\) \(\in\) BC(5; 9) 

5 = 5; 9 = 3²; BCNN(5;9) = 3².5 = 45

\(x\in\) BC(45) = {0; 45; 90; 135; 180; 225; 270; 315; 360; 405;...;}

\(x\) ≤ 400 nên \(x\in\){0; 45; 90; 135; 225; 270; 315; 360; 405}

Bằng bao nhiêu?

(x+2)² +x(x-1)<2x²+1
x²+4x+4+x²-x<2x²+1
3x+4<1
x< -1

Lời giải:
$=16,2\times (5,7+3,7)-6,2\times (4,8+4,8)$

$=16,2\times 9,4-6,2\times 9,6$

$=16,2\times 9,4-6,2\times 9,4-6,2\times 0,2$

$=9,4\times (16,2-6,2)-6,2\times 0,2$

$=9,4\times 10-1,24$

$=94-1,24=92,76$

a) 5x + 7x + x = 169

12x + x = 169

13x = 169

x = 169 : 13

x = 13

b) x + x + x - 2 = 13

3x - 2 = 13

3x = 13 + 2

3x = 15

x = 15 : 3

x = 5