# How do you solve x-5y=4 and 4x+8y=-5 using substitution?

Mar 11, 2016

$x = \frac{1}{4} , y = - \frac{3}{4}$

#### Explanation:

Begin by labelling the equations- easier to follow.

x - 5y = 4 ................................(A)

4x + 8y = -5 ..............................(B)

Rearrange (A) to obtain : x = 4 + 5y ...................(C)

Now substitute this for x in (B)
4(4 + 5y ) + 8y = -5 → 16 + 20y+8y = -5 → $y = - \frac{21}{28} = - \frac{3}{4}$
now substitute $y = - \frac{3}{4} \text{ in } \left(C\right)$
$x = 4 + 5 \times \left(- \frac{3}{4}\right) = \frac{1}{4}$
Check by substituting values of x and y in (A) and (B)