Question

Solve for x: 2 over 5 (x − 4) = 2x.

Answer 1

For this case we must solve the following equation:

$\frac {2} {5 (x-4)} = 2x\\\frac {2} {5x-20)} = 2x$

We multiply on both sides by 5x-20:

$2 = 2x (5x-20)\\2 = 10x ^ 2-40x\\-10x ^ 2 + 40x + 2 = 0\\-5x ^ 2 + 20x + 1 = 0$

We apply the quadratic formula:

$x = \frac {-b \pm \sqrt {b ^ 2-4 (a) (c)}} {2a}$

Where:

$a = -5\\b = 20\\c = 1$

So:

$x = \frac {-20 \pm \sqrt {20 ^ 2-4 (-5) (1)}} {2 (-5)}\\x = \frac {-20 \pm \sqrt {400 + 20}} {- 10}\\x = \frac {-20 \pm \sqrt {420}} {- 10}\\x = \frac {-20 \pm \sqrt {4 * 105}} {- 10}\\x = \frac {-20 \pm2 \sqrt {105}} {- 10}$

Thus, we have two roots:

$x_ {1} = \frac {-10+ \sqrt {105}} {- 5} = \frac {10- \sqrt {105}} {5}\\x_ {2} = \frac {-10- \sqrt {105}} {- 5} = \frac {10+ \sqrt {105}} {5}$

Answer:

$x_ {1} = \frac {10- \sqrt {105}} {5}\\x_ {2} = \frac {10+ \sqrt {105}} {5}$

Answer 2

Answer:

x=-1

Step-by-step explanation:

2/5(x-4)=2x

Multiply both sides by 5

2(x-4) = 10x

2x-8=10x

-8=8x

-1=x

Check :

2/5(-1-4) = 2*-1

2(-1-4)= -10

-10 = -10