Simple equation

Algebra Level 1

x + y = 4 x y = 2 \begin{aligned} x + y &= 4\\ x - y &= 2 \end{aligned}

Find the solution ( x , y ) (x,y) satisfying the 2 equation above.

( 2 , 1 ) (2,1) ( 3 , 1 ) (3,1) ( 3 , 2 ) (3, 2) ( 5 , 3 ) (5, 3)

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7 solutions

Solution 1: By elimination method

x + y = 4 x+y=4 ( 1 ) \color{#D61F06}(1)

x y = 2 x-y=2 ( 2 ) \color{#D61F06}(2)

Adding ( 1 ) \color{#D61F06}(1) and ( 2 ) \color{#D61F06}(2) , we get

2 x = 6 2x=6

Dividing both sides by 2 2 , we get x = 3 \boxed{x=3}

Substitute x = 3 x=3 in any of the two equations. In here I will substitute in ( 2 ) \color{#D61F06}(2) , we have

3 y = 2 3-y=2

Add y y to both sides of the equation. We have,

3 y + y = 2 + y 3-y+y=2+y

3 = 2 + y 3=2+y

Subtract 2 2 from both sides of the equation. We have,

3 2 = 2 2 + y 3-2=2-2+y

1 = y 1=y or y = 1 \boxed{y=1}

a n s w e r : ( 3 , 1 ) answer:(3,1)

Solution 2: By substitution method

Solve for x x in terms of y y in ( 1 ) \color{#D61F06}(1) , then substitute in ( 2 ) \color{#D61F06}(2) . We have,

x + y = 4 x+y=4 \implies x = 4 y x=4-y

Substitute x = 4 y x=4-y in ( 2 ) \color{#D61F06}(2) . We have,

x y = 2 x-y=2

4 y y = 2 4-y-y=2

4 2 y = 2 4-2y=2

Subtract 4 4 from both sides of the equation. We have,

4 4 2 y = 2 4 4-4-2y=2-4

2 y = 2 -2y = -2

Divide both sides by 2 -2 . We get

y = 1 \boxed{y=1}

It follows that, x = 4 y = 4 1 = x=4-y=4-1= 3 \boxed{3}

a n s w e r : ( 3 , 1 ) answer:(3,1)

The confusion people have here is with the substitution method on step 2 perhaps, where you end up with 4-y-y=2. also the calculator shows -2 / 2 = -1 the calculator shows the correct answer if you type (-2) / (-2). Check out: https://www.helpingwithmath.com/by subject/integers/int rules.htm | Same is a plus, different is a negative.

John Bay - 1 year, 4 months ago
Munem Shahriar
Apr 14, 2017

Relevant wiki: Systems of Linear Equations - Elimination

x + y = 4.....................................(1)

x - y = 2......................................(2)

From equation (2),

x = y + 2.......................................(3)

Placing the value of x to equation (1) we get, [ From equation (3)]

y + 2 + y = 4

=> 2y + 2 = 4

=> 2y = 4 - 2

=> 2y = 2

=> y = 2 2 \frac{2}{2}

=> y = 1

Now, placing y = 1 in equation (3)

y = 1+ 2

x = 3

(x, y) = (3, 1)

Answer: (3,1)

Tapas Mazumdar
Apr 14, 2017

Relevant wiki: Systems of Linear Equations - Elimination

{ x + y = 4 x y = 2 \begin{cases} x+y = 4 \\ x - y = 2 \end{cases}

Adding both equations gives

2 x = 6 x = 3 2x = 6 \implies x=3

Subtracting the bottom equation from the top one gives

2 y = 2 y = 1 2y = 2 \implies y=1

Hence the solution is ( 3 , 1 ) \boxed{(3,1)} .

Mohammad Khaza
Jul 11, 2017

x + y = 4.....................................(1)

x - y = 2......................................(2)

so, 2x= 6.............................[subtracting equation 2 from equation 1]

or,x=3

now, 3+y =4......................................(1)

or, y=1

Arthon Godito
Apr 10, 2019

given:

x+y=4

x-y=2

First let's focus on the second equation,we need to find the value of x, to find x, transpose y to the right side of the equation we get

x=2+y

then insert the value of x to first equation making it

(2+y)+y=4

2+y+y=4

2+2y=4

transpose positive 2 to the right side of the equation making it

2y=4-2

2y=2

y=1

we get the value of y lets go back to the equation x=2+y

x=2+(1)

x=3

we find that the value of x is 3, since coordinates come in pairs (x,y) the ordered pair is (3,1)

note: to transpose terms to other side of the equation, you need to take the opposite operation in both sides of the equation.

Oon Han
Dec 9, 2018

x + y = 4 x y = 2 x + y = 4 \\ x - y = 2 If we add the two equations together we will get 2 x = 2 2x = 2 , meaning that x = 1 x = 1 .

Hence. 1 + y = 4 1 + y = 4 , and so y = 3 y = 3 . The solution to the simultaneous equations is ( 3 , 1 ) \boxed{(3, 1)} .

Therefore, the answer is ( 3 , 1 ) (3, 1) .

Aaryan Maheshwari
Aug 24, 2017

We have been given x+y=4 and only (3,1) in the options satisfy this!

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