Question

If x + 4y = 18 and x − 4y = 2, then x = ?

Answer 1

Answer:

x=10

Step-by-step explanation:

We have the system $\left \{ {{x+4y=18} \atop {x-4y=2}} \right.$ and we have to find the value of x,

we can clear y from both equations and then match them.

First equation:

$x+4y=18\\4y=18-x\\y=\frac{18-x}{4}$

Second equation:

$x-4y=2\\4y=x-2\\y=\frac{x-2}{4}$

Now matching both equations:

$y=y\\\frac{18-x}{4}=\frac{x-2}{4}\\18-x=x-2$

We can subtract x in both sides,

$18-x=x-2\\18-x-x=x-2-x\\18-2x=-2$

Subtract 18 in both sides,

$18-2x=-2\\18-2x-18=-2-18\\-2x=-20$

Divide both sides in (-2),

$-2x=-20\\\frac{-2x}{-2} =\frac{-20}{-2}\\ x=10$

Result: x=10

Answer 2

x + 4y = 18 and x − 4y = 2

I would use substitution

add the 2 equations together

  x + 4y = 18

+ x − 4y = 2

-------------------------

2x + 0y = 20

2x = 20

divide each side by 2

2x/2 = 20/2

x = 10

Answer: x=1