Examples with solutions for Sum and Difference of Angles: Using ratios for calculation

Exercise #1

What is the relationship between angle α and β according to the drawing?

αβ = 100°

Step-by-Step Solution

To solve this problem, we need to understand the relationship between the angles α\alpha and β\beta given in the diagram.

Step 1: Determine the relationship between α\alpha and β\beta. The angles α\alpha and β\beta appear to be supplementary, forming a straight line. Hence, their sum is 180180^\circ.

Step 2: Use the given information to calculate α\alpha. Given β=100\beta = 100^\circ, we have:

α=180β=180100=80.\alpha = 180^\circ - \beta = 180^\circ - 100^\circ = 80^\circ.

Step 3: Calculate the ratio α:β\alpha:\beta.

Ratio of α to β=αβ=80100=45.\text{Ratio of } \alpha \text{ to } \beta = \frac{\alpha}{\beta} = \frac{80}{100} = \frac{4}{5}.

Step 4: Express the ratio in the required form, which is a multiple-choice problem comparing given choices:

Therefore, the relationship between angle α\alpha and β\beta according to the drawing is 4:5.

Answer

4:5

Exercise #2

B ∢B is 2 times bigger than A ∢A andC ∢C is 3 times bigger than B ∢B .

Calculate A ∢A .

AAABBBCCC3B

Video Solution

Step-by-Step Solution

To solve this problem, let's calculate A ∢A with the steps outlined below:

  • Step 1: Write the equations for each angle based on the given conditions: B=2A ∢B = 2A C=3B=3(2A)=6A ∢C = 3B = 3(2A) = 6A

  • Step 2: Use the sum of angles in a triangle: A+B+C=180 ∢A + ∢B + ∢C = 180^\circ Substitute the expressions: A+2A+6A=180 A + 2A + 6A = 180

  • Step 3: Simplify the equation: 9A=180 9A = 180 Divide both sides by 9 to solve for AA: A=1809=20 A = \frac{180}{9} = 20

Therefore, the solution to the problem is A=20 ∢A = 20^\circ .

Answer

20°

Exercise #3

The triangle ABC is shown below.

angle A=70° ∢A=70° .

BC=13 \frac{∢B}{∢C}=\frac{1}{3}

Calculate angle C ∢C .

AAABBBCCC70°

Video Solution

Step-by-Step Solution

To solve this problem, we'll use the properties of a triangle and given ratio:

  • Step 1: Let B=x ∢B = x and C=3x ∢C = 3x as per the given ratio BC=13 \frac{∢B}{∢C} = \frac{1}{3} .
  • Step 2: Use the triangle sum property: A+B+C=180 ∢A + ∢B + ∢C = 180^\circ .
  • Step 3: Substitute known values: 70+x+3x=180 70^\circ + x + 3x = 180^\circ .
  • Step 4: Simplify: 4x+70=180 4x + 70^\circ = 180^\circ .
  • Step 5: Solve for x x : 4x=110 4x = 110^\circ .
  • Step 6: Determine x x : x=27.5 x = 27.5^\circ .
  • Step 7: Calculate C ∢C : C=3x=3×27.5=82.5 ∢C = 3x = 3 \times 27.5^\circ = 82.5^\circ .

Therefore, the measure of angle C ∢C is 82.5 82.5^\circ .

Answer

82.5°

Exercise #4

One angle in a triangle is 90°.
The ratio between the other two angles is 2:1.

What are the sizes of the other angles in the triangle?

Step-by-Step Solution

To solve this problem, let's follow these steps:

  • Step 1: Identify the given information; one angle is 9090^\circ, and the other two angles are in a 2:1 ratio.
  • Step 2: Set up an equation using the relationship between the angles: 90+2x+x=18090^\circ + 2x + x = 180^\circ.
  • Step 3: Solve the equation for xx.
  • Step 4: Calculate the measures of the two angles.

Now, let's work through each step.
Step 1: Given a right triangle, one angle is 9090^\circ, and the other two angles are in the ratio 2:1.

Step 2: Express the other two angles in terms of xx:
- One angle is 2x2x.
- The second angle is xx.

Step 3: Use the sum of angles in a triangle to write an equation:
90+2x+x=18090^\circ + 2x + x = 180^\circ.

Step 4: Simplify and solve the equation:
Combine like terms:
90+3x=18090^\circ + 3x = 180^\circ.

Subtract 9090^\circ from both sides:
3x=903x = 90^\circ.

Divide both sides by 3:
x=30x = 30^\circ.

Now we can find the measures of the other angles:
The angle expressed as xx is 3030^\circ.
The angle expressed as 2x2x is 2×30=602 \times 30^\circ = 60^\circ.

Therefore, the solution is that the other two angles are 6060^\circ and 3030^\circ.

Answer

60°, 30°