Question

A-b+2c=7 b+c=1 a-2b-3c=0

Answer 1

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!~