SOLUTION: I saw this problem in my math book: The perimeter of the parallelogram below is 42 meters. Write a linear equation in two variables for the perimeter. Use this equation to find

Question 307528: I saw this problem in my math book:
The perimeter of the parallelogram below is 42 meters. Write a linear equation in two variables for the perimeter. Use this equation to find x when y is 8.
2y
x x
2y
My answer is: 2x+4y=42 and I get the right answer. I know the perimeter of a parallelogram is P=2a+2b.
The book's answer is: x+y=21 and get the same answer I do (x = 5 meters)
My question is why does the book use the equation, x+y=21, for the answer????
Answer by Earlsdon(6294) (Show Source): You can put this solution on YOUR website!
Assuming that x and y are the lengths of the sides of the parallelogram, then the perimeter is given by:
Substituting we have...
Factoring a 2 from the right side then dividing both sides by 2, we get...
or
Now if y = 8, then...
Subtracting 8 from both sides, we get...

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