McGraw Hill Integrated II, 2012
MH
McGraw Hill Integrated II, 2012 View details
4. Rectangles
Continue to next subchapter

Exercise 56 Page 511

Recall the theorem, which tells us that if a quadrilateral is a parallelogram then its opposite sides are congruent.

x=2
y=7

Practice makes perfect

We want to find the values of x and y for which the given quadrilateral is a parallelogram, using the given algebraic expressions for the lengths of the half-diagonals.

Recall the following theorem.

Converse Parallelogram Diagonals Theorem

If the diagonals of a quadrilateral bisect each other, then the quadrilateral is a parallelogram.

Therefore, for the quadrilateral to be a parallelogram, the segments with the following lengths are congruent. 4y-9 = 2y+5 and y+3 = 2x+6 Let's create a system of equations by substituting the lengths of the segments into these equations. 4y-9=2y+5 y+3=2x+6 To solve it we will use the Substitution Method.
4y-9=2y+5 & (I) y+3=2x+6 & (II)
4y-9=2y+5 & (I) y=2x+3 & (II)
4( 2x+3)-9=2( 2x+3)+5 y=2x+3
(I): Solve for y
8x+12-9=4x+6+5 y=2x+3
8x+3=4x+11 y=2x+3
8x=4x+8 y=2x+3
4x=8 y=2x+3
x=2 y=2x+3
Now that we have found x, we can substitute it in the second equation to find y.
x=2 y=2x+3
x=2 y=2 2+3
x=2 y=4+3
x=2 y=7