Pearson Geometry Common Core, 2011
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Pearson Geometry Common Core, 2011 View details
3. Proving Triangles Similar
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Exercise 40 Page 458

Recall the classification of quadrilaterals. You can begin by finding the slopes of the sides.

Square, see solution.

Practice makes perfect

Let's plot the given points on a coordinate plane and graph the quadrilateral.

To determine the most precise name for our quadrilateral, let's review the classification of quadrilaterals.
Quadrilateral Definition
Parallelogram Both pairs of opposite sides are parallel
Rhombus Parallelogram with four congruent sides
Rectangle Parallelogram with four right angles
Square Parallelogram with four congruent sides and four right angles
Trapezoid Quadrilateral with exactly one pair of parallel sides
Isosceles Trapezoid Trapezoid with legs that are congruent
Kite Quadrilateral with two pairs of consecutive sides congruent and no opposite sides congruent

Now, let's find the slopes of the sides using the Slope Formula.

Side Slope Formula Simplified
Slope of AB: ( 2,4), ( 4,6) 6- 4/4- 2 1
Slope of BC: ( 4,6), ( 6,4) 4- 6/6- 4 - 1
Slope of CD: ( 6,4), ( 4, 2) 2- 4/4- 6 1
Slope of DA: ( 4, 2), ( 2,4) 4- 2/2- 4 - 1

We can tell that the slopes of the opposite sides of our quadrilateral are equal. Therefore, both pairs of opposite sides are parallel and the quadrilateral is a parallelogram. We can also tell that the consecutive side are perpendicular, as their slopes are opposite reciprocals. 1 ( - 1) = -1 Therefore, our quadrilateral is either a rectangle or a square. To check, we can find the lengths of its sides using the Distance Formula.

Side Distance Formula Simplified
Length of AB: ( 2,4), ( 4,6) sqrt(( 4- 2)^2+( 6- 4)^2) 2sqrt(2)
Length of BC: ( 4,6), ( 6, 4) sqrt(( 6- 4)^2+( 4- 6)^2) 2sqrt(2)
Length of CD: ( 6,4), ( 4,2) sqrt(( 4- 6)^2+( 2- 4)^2) 2sqrt(2)
Length of DA: ( 4, 2), ( 2,4) sqrt(( 2- 4)^2+( 4- 2)^2) 2sqrt(2)

Our parallelogram has four congruent sides. Therefore, the most precise name for this quadrilateral is a square.