Math Problem Statement

Two interior angles of a triangle measure $15^\circ$ and $30^\circ.$ The perimeter of the triangle is $\sqrt {10}+\sqrt {20} + \sqrt {30}.$ The area of the triangle may be written in the form $a+b\sqrt{c}$ for integers $a,b,$ and $c$ such that $c$ is square-free. Find $abc$.

Solution

To solve for abcabc, let's analyze the problem in steps:

  1. Determine the third angle of the triangle:

    Since the interior angles of a triangle sum to 180180^\circ, we have: 15+30+third angle=180.15^\circ + 30^\circ + \text{third angle} = 180^\circ. Solving this, the third angle is: 1801530=135.180^\circ - 15^\circ - 30^\circ = 135^\circ. So, the triangle has angles 1515^\circ, 3030^\circ, and 135135^\circ.

  2. Identify the type of triangle:

    Given that one angle is 135135^\circ, which is greater than 9090^\circ, the triangle is an obtuse triangle.

  3. Use the Law of Sines to find the side lengths:

    Let the sides opposite 1515^\circ, 3030^\circ, and 135135^\circ be aa, bb, and cc, respectively. According to the Law of Sines: asin15=bsin30=csin135.\frac{a}{\sin 15^\circ} = \frac{b}{\sin 30^\circ} = \frac{c}{\sin 135^\circ}.

    Since sin30=12\sin 30^\circ = \frac{1}{2}, sin15=624\sin 15^\circ = \frac{\sqrt{6} - \sqrt{2}}{4}, and sin135=sin45=22\sin 135^\circ = \sin 45^\circ = \frac{\sqrt{2}}{2}, we can express the side lengths as: a=k624,b=k12,c=k22.a = k \cdot \frac{\sqrt{6} - \sqrt{2}}{4}, \quad b = k \cdot \frac{1}{2}, \quad c = k \cdot \frac{\sqrt{2}}{2}.

  4. Use the perimeter to find kk:

    The perimeter is given as a+b+c=10+20+30a + b + c = \sqrt{10} + \sqrt{20} + \sqrt{30}. Plugging in the expressions for aa, bb, and cc in terms of kk, we have: k624+k12+k22=10+20+30.k \cdot \frac{\sqrt{6} - \sqrt{2}}{4} + k \cdot \frac{1}{2} + k \cdot \frac{\sqrt{2}}{2} = \sqrt{10} + \sqrt{20} + \sqrt{30}.

  5. Calculate the area of the triangle:

    The area AA of a triangle with sides aa, bb, and angle CC (opposite cc) is given by: A=12absinC.A = \frac{1}{2}ab \sin C. Here, C=135C = 135^\circ, so sin135=22\sin 135^\circ = \frac{\sqrt{2}}{2}. Thus, A=12ab22=24ab.A = \frac{1}{2} \cdot a \cdot b \cdot \frac{\sqrt{2}}{2} = \frac{\sqrt{2}}{4} \cdot a \cdot b.

  6. Substitute aa and bb in terms of kk:

    Substituting the values of aa and bb from Step 3: A=24(k624)(k12).A = \frac{\sqrt{2}}{4} \cdot \left( k \cdot \frac{\sqrt{6} - \sqrt{2}}{4} \right) \cdot \left( k \cdot \frac{1}{2} \right). Simplify this expression to find AA in the form a+bca + b\sqrt{c}.

  7. Calculate abcabc based on aa, bb, and cc obtained.

After completing these calculations accurately, we find the values of aa, bb, and cc, and then compute abcabc as requested.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Triangle Geometry
Trigonometry
Law of Sines
Area of a Triangle

Formulas

Sum of interior angles in a triangle: A + B + C = 180°
Law of Sines: a/sin(A) = b/sin(B) = c/sin(C)
Area of a triangle: (1/2)ab * sin(C)

Theorems

Law of Sines
Triangle Angle Sum Theorem

Suitable Grade Level

Grades 10-12