Equation 1) a - b + 2c = 7
Equation 2) b + c = 1
Equation 3) a - 2b - 3c = 0
Subtract equation 3 from equation 1.
3) a - 2b - 3c = 0
1) a - b + 2c = 7
Subtract equations from one another.
-b - 5c = -7 {This will now be called equation 4)
Then, add equation 4 into equation 2.
4) -b - 5c = -7
2) b + c = 1
Add.
-4c = -6
Divide both sides by -4.
c = 3/2
Plug in 3/2 for c in the 2nd equation.
2) b + c = 1
b + (3/2) = 1
Subtract 3/2 from both sides.
b = 1 - 3/2
Simplify.
b = 1 - 1 1/2
Simplify.
b = -1/2
Plug in -1/2 for b in equation 1 so that we find the value of a.
*Remember : b = -1/2, c = 3/2
1) a + b + 2c = 7
Plug in -1/2 for b, and plug in 3/2 for c.
a + (-1/2) + 2(3/2) = 7
Simplify.
a - 1/2 + 3 = 7
Simplify.
a - 2 1/2 = 7
Add 2 1/2 to both sides.
a = 7 + 2 1/2
Simplify.
a = 9 1/2
So, a = 9 1/2, b = -1/2, c = 3/2
~Hope I helped!~