Big Ideas Math Integrated I, 2016
BI
Big Ideas Math Integrated I, 2016 View details
1. Angles of Triangles
Continue to next subchapter

Exercise 10 Page 592

To classify the triangle by its sides, you need to know their lengths. To determine if the triangle is a right triangle, you need to know the slopes of the sides.

Classify by sides: Scalene triangle
Right triangle? Yes

Practice makes perfect

Let's start by drawing the triangle in a coordinate plane.

Now we can classify the triangle by calculating the side lengths, and then we can determine if it is a right triangle.

Classify by Sides

To classify a triangle by its sides, first we need to calculate the length of the sides using the Distance Formula. Let's start by finding the distance between A( -2, 3) and B( 0, -3). This will give us the value of AB.
d_(AB) = sqrt((x_2 - x_1)^2 + (y_2 - y_1)^2)
d_(AB) = sqrt(( 0 - ( -2))^2 + ( -3 - 3)^2)
Evaluate right-hand side
d_(AB) = sqrt(2^2 + (-3-3)^2)
d_(AB) = sqrt(2^2 + (-6)^2)
d_(AB) = sqrt(4 + 36)
d_(AB) = sqrt(40)
d_(AB) = sqrt(4* 10)
d_(AB) = sqrt(4) * sqrt(10)
d_(AB) = 2 sqrt(10)
We can find the lengths of the other sides in the same way.
Side Points sqrt((x_2-x_1)^2+(y_2-y_1)^2) Length
AB ( -2,3) & ( 0,-3) sqrt(( 0-( -2))^2+( -3- 3)^2) 2sqrt(10)
AC ( -2,3) & ( 3,-2) sqrt(( 3-( -2))^2+( -2-( 3))^2) 5sqrt(2)
BC ( 0,-3) & ( 3,-2) sqrt(( 3- 0)^2+( -2-( -3))^2) sqrt(10)

As we can see, all the lengths are different. This means △ ABC is scalene.

Right Triangle?

In our diagram, we see that ∠ A and ∠ C are acute angles. In order for △ ABC to be a right triangle, ∠ B must be a right angle. To determine if this is the case, we will first calculate the slope of AB and BC using the Slope Formula.

Side Points y_2-y_1/x_2-x_1 Slope Simplified Slope
AB ( - 2,3) & ( 0,-3) -3- 3/0-( - 2) - 6/2 - 3
BC ( 0,-3) & ( 3,-2) -2-( -3)/3- 0 1/3 1/3

Since -3 and 13 are opposite reciprocals, we know that AB is perpendicular to BC. Therefore, △ ABC is in fact a right triangle.