Question

x + 2 = y + a
y - z = a - 5
z = x - 2 + a

According to the system of equations above, what is the value of a?

Answer 1

Take the first equation, and subtract 2 from both sides.
x + 2 = y + a
x + 2 -2 = y + a -2
x = y + a -2

substitute y + a -2 for x, into 3rd equation.

z = x - 2 + a ----> z = (y + a -2) - 2 + a ---> z=y+a

So now we have two equations.
y - z = a - 5
z=y+a

subtract y from both sides in a second equation.
z-y=y-y+a
z-y=a

so now we have

y - z = a - 5 and
z-y=a

multiply the second equation by -1
y-z=-a

we know that
y-z= -a and
y-z = a - 5

so we can say that

-a=a-5
subtract a from both sides,
-2a=5

divide both sides by 2
a= -5/2

Answer 2

Do you need more help understanding this?

Answer 3

-a=a-5
-2a = -5
a = 5/2
not -5/2
@SolomonZelman