a: \(\Leftrightarrow2x^3-56-7x^2+16x=0\)

\(\Leftrightarrow2x\left(x^2+8\right)-7\left(x^2+8\right)=0\)

=>2x-7=0

hay x=7/2

b: \(\Leftrightarrow x^5\left(x^2+2\right)+x\left(x^2+2\right)=0\)

=>x(x²+2)(x⁴+1)=0

=>x=0

c: \(\Leftrightarrow2x^2+x-5x-\dfrac{5}{2}=0\)

\(\Leftrightarrow2x^2-4x-\dfrac{5}{2}=0\)

hay \(x\in\left\{\dfrac{5}{2};-\dfrac{1}{2}\right\}\)

\(2^x+2^{x+1}+2^{x+2}=56\)

\(2^x+2^x.2+2^x.2^2=56\)

\(2^x.\left(1+2+4\right)=56\)

\(2^x.7=56\)

\(2^x=8\)

\(=>2^x=2^3\)

\(=>x=3\)

`2^x+2^x*2+2^x*2^2=56`

`2^x+2^x*2+2^x*4=56`

`2^x*(1+2+4)=56`

`2^x*7=56`

`2^x=56 \div 7`

`2^x=8`

`2^x=2^3`

`-> x=3`

a) Ta có 2^x + 2^{x + 1} + 2^{x + 2} = 56

⇒ 2^x ( 1 + 2¹ + 2² ) = 56

⇒ 2^x . 7 = 56

⇒ 2^x = 56 : 7 = 8 = 2³

Vậy x = 3

b) Ta có 3^x + 3^{x + 2} + 3^{x + 3} = 111

⇒ 3^x ( 1 + 3² + 3³ ) = 111

⇒ 3^x . 37 = 111

⇒ 3^x = 111 : 37 = 3 = 3¹

Vậy x = 1

Cho mk sửa lại ở câu c là 2^n+2 + 2^n+1  - 2^n = 56 nha!

a)  \(7x^2-16x=2x^3-56\)

\(\Leftrightarrow\)\(2x^3-7x^2+16x-56=0\)

\(\Leftrightarrow\)\(2x\left(x^2+8\right)-7\left(x^2+8\right)=0\)

\(\Leftrightarrow\)\(\left(2x-7\right)\left(x^2+8\right)=0\)

\(\Leftrightarrow\)\(2x-7=0\)

\(\Leftrightarrow\)\(x=3,5\)

Vậy...

b)  \(x^7+x^3+2x^5+2x=0\)

\(\Leftrightarrow\)\(x.\left(x^6+x^2+2x^4+2\right)=0\)

\(\Leftrightarrow\)\(x\left(x^2+2\right)\left(x^4+1\right)=0\)

\(\Leftrightarrow\)\(x=0\)

Vậy...

c)  \(\left(2x+1\right)x-5\left(x+\frac{1}{2}\right)=0\)

\(\Leftrightarrow\)\(2x\left(x+\frac{1}{2}\right)-5\left(x+\frac{1}{2}\right)=0\)

\(\Leftrightarrow\)\(\left(2x-5\right)\left(x+\frac{1}{2}\right)=0\)

\(\Leftrightarrow\)\(\orbr{\begin{cases}2x-5=0\\x+\frac{1}{2}=0\end{cases}}\)

\(\Leftrightarrow\)\(\orbr{\begin{cases}x=2,5\\x=-0,5\end{cases}}\)

Vậy...

1.

\(\left(2x+3^{ }\right)^4=16\)

⇔\(\left(2x+3\right)^4=2^4\)

⇔\(2x+3=2\)

⇔\(2x=5\)

⇔\(x=\frac{5}{2}\)

Vậy....

a, 2x - (-9) = x-(-15)

2x + 9 = x+15

2x - x = 15 -9

x = 6

b, 56 + 5x = 2x + 11

5x - 2x = 11 - 56

3x = -45

x = (-45) : 3

x = -15

a) 2x - (-9) = x - (-15)

=> 2x +9 = x + 15

=> 2x - x = 15 - 9

=> x(2-1) = 6

=> x.1 = 6

b) 56 + 5x = 2x + 11

=> 5x -2x = 11 - 56

=> x (5-2) = -45

=> x.3 = -45

=> x = -45: 3

=> x = -15

1.

Áp dụng tính chất dãy tỉ số bằng nhau:

$\frac{x}{5}=\frac{y}{7}=\frac{z}{10}=\frac{2x}{10}=\frac{y}{7}=\frac{z}{10}$

$=\frac{2x+y-z}{10+7-10}=\frac{-21}{7}=-3$

$\Rightarrow x=-3.5=-15; y=-3.7=-21; z=-3.10=-30$

2.

Áp dụng tính chất dãy tỉ số bằng nhau:

$\frac{x}{3}=\frac{y}{4}=\frac{z}{6}=\frac{2x}{6}=\frac{4y}{16}=\frac{3z}{18}$

$=\frac{4y-2x+3z}{16-6+18}=\frac{-56}{28}=-2$

$\Rightarrow x=-2.3=-6; y=-2.4=-8; z=-2.6=-12$