x + y x − y = 4 = 2
Find the solution ( x , y ) satisfying the 2 equation above.
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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.
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
=> y = 1
Now, placing y = 1 in equation (3)
y = 1+ 2
x = 3
(x, y) = (3, 1)
Answer: (3,1)
Relevant wiki: Systems of Linear Equations - Elimination
{ x + y = 4 x − y = 2
Adding both equations gives
2 x = 6 ⟹ x = 3
Subtracting the bottom equation from the top one gives
2 y = 2 ⟹ y = 1
Hence the solution is ( 3 , 1 ) .
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
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.
x + y = 4 x − y = 2 If we add the two equations together we will get 2 x = 2 , meaning that x = 1 .
Hence. 1 + y = 4 , and so y = 3 . The solution to the simultaneous equations is ( 3 , 1 ) .
Therefore, the answer is ( 3 , 1 ) .
We have been given x+y=4 and only (3,1) in the options satisfy this!
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Solution 1: By elimination method
x + y = 4 ( 1 )
x − y = 2 ( 2 )
Adding ( 1 ) and ( 2 ) , we get
2 x = 6
Dividing both sides by 2 , we get x = 3
Substitute x = 3 in any of the two equations. In here I will substitute in ( 2 ) , we have
3 − y = 2
Add y to both sides of the equation. We have,
3 − y + y = 2 + y
3 = 2 + y
Subtract 2 from both sides of the equation. We have,
3 − 2 = 2 − 2 + y
1 = y or y = 1
a n s w e r : ( 3 , 1 )
Solution 2: By substitution method
Solve for x in terms of y in ( 1 ) , then substitute in ( 2 ) . We have,
x + y = 4 ⟹ x = 4 − y
Substitute x = 4 − y in ( 2 ) . We have,
x − y = 2
4 − y − y = 2
4 − 2 y = 2
Subtract 4 from both sides of the equation. We have,
4 − 4 − 2 y = 2 − 4
− 2 y = − 2
Divide both sides by − 2 . We get
y = 1
It follows that, x = 4 − y = 4 − 1 = 3
a n s w e r : ( 3 , 1 )