Question

X + 2y = 7x - y = 1Solve for x and y?​

Answer 1

Answer:

y=2

x=3

Step-by-step explanation:

make x - y = 1 into x= y + 1

put that wherever x is in the other equation

so y + 1 + 2y =7. then combine like terms into 3y =6. then divide 6 by 3 so you get y = 2

then substitute 2 into the y in the equation x - y = 1 and you get x = 3

Answer 2

METHOD OF ELIMINATION:

Given pair of linear equations are:

x+2y= 7 – – – Eqn(i)

On comparing with a1x+b1y+c1 = 0

• a1 = 1,
• b1 = 2,
• c1 = -7

x-y = 1 – – – Eqn(ii)

On comparing with a2x+b2y+c2 = 0

• a2 = 1,
• b2 = -1 ,
• c2 = -1

a1/a2 = 1/1 = 1

b1/b2 = 2/-1 = -2

c1/c2 = -7/-1 = 7

We have,

a1/a2 ≠ b1/b2 ≠ c1/c2

So, Given pair of linear equations in two variables have a unique solution.

Now,

On Subtracting eqn(ii) from eqn(i) then

x+2y = 7

x-y = 1

(-)

_______

0 +3y = 6

_______

⇛ 3y = 6

⇛ y = 6/3

⇛ y = 2

On Substituting the value of y in (1) then

⇛ x-2 = 1

⇛ x = 1+2

⇛x = 3

Answer: Therefore , the value of x and y with be (3,2) respectively.

Additional comment:

• If a₁x+b₁y+c₁ = 0 and a₂x+b₂y+c₂ = 0 are pair of linear equations in two variables then
• If a₁/a₂ ≠b₁/b₂ ≠ c₁/c₂ then they are Consistent and independent lines or Intersecting lines and they have a unique solution.
• If a₁/a₂ = b₁/b₂ = c₁/c₂ then they are Consistent and dependent lines or Coincident lines and they have infinitely number of many solutions.
• If a₁/a₂ =b₁/b₂ ≠ c₁/c₂ then they are Inconsistent lines or Parallel lines lines and they have no solution.