Glencoe Math: Course 3, Volume 2
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Glencoe Math: Course 3, Volume 2 View details
2. Congruence
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Exercise 6 Page 525

See solution.

Practice makes perfect

In the following figure, triangle EFG is congruent to triangle LMN.

We want to find the value of x, then describe the transformations that map △ EFG onto △ LMN. Let's begin by finding the value of x.

Finding the value of x

Note that the corresponding sides of the congruent triangles are congruent. △ EFG ≅ △ LMN ⇓ Congruent Sides [0.5em] EF≅LM FG≅MN EG≅LN Segment MN is congruent to segment FG. This means that we can find the length of FG and equate it to the length of MN to find x. Notice that △ EFG is a right triangle. This means that we can use the Pythagorean Theorem to find the missing length of the hypotenuse FG. In this triangle, the lengths of the legs are 5 centimeters and 12 centimeters.
EF^2+EG^2=FG^2
5^2+ 12^2=FG^2
Solve for FG
25+144=FG^2
169=FG^2
13*13=FG^2
13^2=FG^2
sqrt(13^2)=sqrt(FG^2)
13=FG
FG=13
We found that the length of FG is 13 centimeters. Let's use this information to find the value of x. NM&=x+3 & ⇒ x+3=13 FG&=13 We will solve this equation for x.
x+3=13
x=10
The value of x is 10. Now we will describe the transformations that map △ EFG onto △ LMN.

Identifying the Transformations

The orientation of the triangle is different, so we can first rotate △ EFG 180^(∘) clockwise about vertex G.

Next we need to translate the image of the rotation up to overlap with △ LMN.

One series of transformations that maps △ EFG onto △ LMN is a 180^(∘) clockwise rotation followed by an upward translation. Please note that this is just one example of a series of transformations and that there are many other possibilities.