Question

Solve by substitute
{ 5x+4y=12
{3x+4y=4
Please help

Answer 1

5x + 4y = 12
4y = -5x + 12
y = -5/4x + 3

now sub -5/4x + 3 in for y into the other equation

3x + 4y = 4
3x + 4(-5/4x + 3) = 4
3x - 5x + 12 = 4
3x - 5x = 4 - 12
-2x = - 8
x = 4

now sub 4 in for x in either equation to find y
5x + 4y = 12
5(4) + 4y = 12
20 + 4y = 12
4y = 12 - 20
4y = - 8
y = -2

now we check..
3x + 4y = 4
3(4) + 4(-2) = 4
12 - 8 = 4
4 = 4 (correct)

answer is : x = 4 and y = -2 or (4,-2)