Big Ideas Math Geometry, 2014
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Big Ideas Math Geometry, 2014 View details
1. Angles of Triangles
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Exercise 45 Page 238

Practice makes perfect
a Isosceles triangles have two congruent sides. Therefore, we need to consider three cases.

Let's consider them one at a time.

AB≅ BC

Here we have that AB ≅ BC.

If two sides are congruent, then they have the same measure. AB=BC ⇒ x=2x-4 Let's solve the above equation.
x=2x-4
- x=- 4
x=4
We can now find the values of AB and BC. AB:& x ⇒ 4 BC:& 2x-4 ⇒ 2( 4)-4=4 Knowing that both AB and BC are 4, and that the perimeter is 32, we can find the value of CA.
AB+BC+CA=32
4+ 4+CA=32
8+CA=32
CA=24
Let's try to draw a triangle using segments with these lengths.

This is not a triangle. Since AC is longer than the sum the other two side lengths, it is not possible to make a triangle using these segments.

AB≅ CA

Here we have that AB ≅ CA.

If two sides are congruent, then they have the same measure. AB=CA ⇒ CA=x Knowing that the perimeter is 32, we can write and solve an equation to find the value of x.
AB+BC+CA=32
x+ 2x-4+ x=32
â–Ľ
Solve for x
4x-4=32
4x=36
x=9
We can now find the side lengths of the triangle. AB:& x ⇒ 9 BC:& 2x-4 ⇒ 2( 9)-4=14 CA:& x ⇒ 9 Let's draw the obtained triangle.

We found that when the perimeter is 32, a possible value for x is 9.

BC≅ CA

Here we have that BC ≅ CA.

If two sides are congruent, then they have the same measure. BC=CA ⇒ CA=2x-4 Knowing that the perimeter is 32, we can write and solve an equation to find the value of x.
AB+BC+CA=32
x+ 2x-4+ 2x-4=32
â–Ľ
Solve for x
5x-8=32
5x=40
x=8
We can now find the side lengths of the triangle. AB:& x ⇒ 8 BC:& 2x-4 ⇒ 2( 8)-4=12 CA:& 2x-4 ⇒ 2( 8)-4=12 Let's draw the obtained triangle.

We found that when the perimeter is 32, another possible value for x is 8.

b We need to consider the three cases we considered in Part A, but this time with a perimeter of 12.

AB≅ BC

In Part A, we found that if AB≅ BC, then we could find x by solving the equation x=2x-4. x=2x-4 ⇔ x=4By using the fact that the perimeter is 12, we can find the length of CA.
AB+BC+CA=12
4+ 4+CA=12
8+CA=12
CA=4
Since all sides have the same length we have an equilateral triangle. Therefore, x=4 a possible answer.

AB≅ CA

In this case, both AB and CA are x, and BC is 2x-4. Knowing that the perimeter is 12, we can find the value of x.
AB+BC+CA=12
x+ 2x-4+ x=12
4x-4=12
4x=16
x=4
We obtained the same value as before, x=4.

BC≅ CA

In this case, both BC and CA are 2x-4, and AB is x. Knowing that the perimeter is 12, we can find the value of x.
AB+BC+CA=12
x+ 2x-4+ 2x-4=12
5x-8=12
5x=20
x=4
There is only one value for x that makes the perimeter 12. This value is x=4.