Question

I need help understanding substitution. The problem is: 7x-2y=1. Y=-4

Answer 1

They give you the value of y, y=-4, so you substitute this value for y into the other equation to get...

7x-2(-4)=1 perform indicated multiplication on left side...

7x+8=1 subtract 8 from both sides

7x=-7 divide both sides by 7

x=-1

So the solution to the system of equations is the point (-1,-4)

Answer 2

1 Simplify brackets
7x-2y\times -4=17x−2y×−4=1

2 Simplify 2y\times -42y×−4 to -8y−8y
7x-(-8y)=17x−(−8y)=1

3 Simplify brackets
7x+8y=17x+8y=1

4 Subtract 8y8y from both sides
7x=1-8y7x=1−8y

5 Divide both sides by 77
x=\frac{1-8y}{7}x=
​7
​
​1−8y
​​