Toán

a: \(x\in\left\{21;35;42;49\right\}\)

b: \(x\in\left\{12;54;75\right\}\)

C đáy=(10+10+15+20)=55(cm)

Sxq=55*8=440cm²

a: \(x\in\left\{0;3;6;9\right\}\)

b: x=5

` a) x^2(x-y)+2x-2y `

` = x^2(x-y)+2(x-y) `

` = (x<sup>2</sup>+2)(x-y) `

 ` b) (5x-2y)(5x+2y)+4y-1 `

` = 25x<sup>2</sup>-4y<sup>2</sup>+4y-1 `

` = 25x<sup>2</sup>-(4y<sup>2</sup>-4y+1) `

` = 25x<sup>2</sup>-(2y-1)<sup>2</sup>`

` = (5x-2y+1)(5x+2y-1) `

 ` c) x<sup>2</sup>(xy+1)+2y-x-3xy `
`= x^3y + x^2+2y-x-3xy`
`= x^3y -xy +x^2-x + 2y-2xy`
`= xy.(x^2-1) + x.(x-1) + 2y.(1-x)`
`= xy.(x-1)(x+1) + x.(x-1) -2y.(x-1)`
`= (x-1).[xy.(x+1) + x-2y]`
`= (x-1).(x^2y+1+x-2y)`

56 = 2³.7

140 = 2².5.7

168 = 2³.3.7

ƯCLN(56; 140; 168) = 2².7 = 28

56=2³.7

140=2².5.7

168=2³.3.7

ƯCLN(56;140;168)=2².7=28

a: \(A=x^3-6x^2+12x-8-x^3+4x^2+8\)

\(=-2x^2+12x\)

\(B=x-3-x^2-7x-9=-x^2-6x-12\)

b: Khi x=-1 thì A=-2-12=-14

c: \(C=A+B=-3x^2+6x-12\)

\(=-3\left(x^2-2x+4\right)\)

\(=-3\left(x-1\right)^2-9< 0\)

ko đăng lại!

\(\dfrac{8}{5}-x+\dfrac{4}{5}=\dfrac{6}{3}\)

\(\dfrac{8}{5}-x=2-\dfrac{4}{5}\)

\(\dfrac{8}{5}-x=\dfrac{6}{5}\)

\(x=\dfrac{8}{5}-\dfrac{6}{5}\)

\(x=\dfrac{2}{5}\)

Vậy \(x=\dfrac{2}{5}\)

\(\dfrac{8}{5}-x+\dfrac{4}{5}=\dfrac{6}{3}\)
\(\dfrac{8}{5}-x=\dfrac{6}{3}-\dfrac{4}{5}\)
\(\dfrac{8}{5}-x=\dfrac{30}{15}-\dfrac{12}{15}\)
\(\dfrac{8}{5}-x=\dfrac{18}{15}\)
\(x=\dfrac{8}{5}-\dfrac{18}{15}\)
\(x=\dfrac{24}{15}-\dfrac{18}{15}\)
Vậy \(x=\dfrac{6}{15}\)