The problem requires us to find the lengths of the sides AB, BC, and AC, and the measures of the angles $\angle ABC$, $\angle BAC$, and $\angle ACB$ for the triangle formed by the points A(3, 4), B(1, 1), and C(5, 1).
GeometryTriangleDistance FormulaLaw of CosinesCoordinate GeometryAngle CalculationSide Length Calculation
2025/3/12
1. Problem Description
The problem requires us to find the lengths of the sides AB, BC, and AC, and the measures of the angles ∠ABC, ∠BAC, and ∠ACB for the triangle formed by the points A(3, 4), B(1, 1), and C(5, 1).
2. Solution Steps
First, we calculate the lengths of the sides using the distance formula.
The distance formula between two points (x1,y1) and (x2,y2) is:
d=(x2−x1)2+(y2−y1)2
AB=(1−3)2+(1−4)2=(−2)2+(−3)2=4+9=13≈3.61
BC=(5−1)2+(1−1)2=(4)2+(0)2=16=4
AC=(5−3)2+(1−4)2=(2)2+(−3)2=4+9=13≈3.61
Next, we find the angles using the Law of Cosines.
The Law of Cosines is:
c2=a2+b2−2abcos(C), where a, b, and c are the side lengths, and C is the angle opposite side c.
To find ∠ABC, we use the formula with AC2=AB2+BC2−2(AB)(BC)cos(∠ABC):
13=13+16−2(13)(4)cos(∠ABC)
0=16−813cos(∠ABC)
813cos(∠ABC)=16
cos(∠ABC)=81316=132
∠ABC=cos−1(132)≈56.31∘
To find ∠BAC, we use the formula with BC2=AB2+AC2−2(AB)(AC)cos(∠BAC):
16=13+13−2(13)(13)cos(∠BAC)
16=26−2(13)cos(∠BAC)
16=26−26cos(∠BAC)
26cos(∠BAC)=10
cos(∠BAC)=2610=135
∠BAC=cos−1(135)≈67.38∘
To find ∠ACB, we can use the fact that the sum of angles in a triangle is 180∘: