Example

Finding Right Triangle Angles When One Is Expressed Relative to Another

Apply the geometry problem-solving strategy when the angles of a right triangle are defined relative to one another, requiring an algebraic expression for each before setting up the equation.

Problem: The measure of one angle of a right triangle is 4040 degrees more than the measure of the smallest angle. Find the measures of all three angles.

  1. Read the problem.
  2. Identify what you are looking for: the measures of all three angles.
  3. Name: Choose a variable to represent the smallest angle. Let aa be the measure of the first (smallest) angle. Since the second angle is 4040 degrees more, its measure is a+40a + 40. The third angle is a right angle, meaning its measure is 9090. Draw the figure and label it with these expressions.
  4. Translate: Write the appropriate formula (the triangle angle sum property) and substitute the expressions: a+(a+40)+90=180a + (a + 40) + 90 = 180
  5. Solve the equation. Combine like terms: 2a+130=1802a + 130 = 180. Subtract 130130 from both sides: 2a=502a = 50. Divide by 22: a=25a = 25. Substitute aa to find the other angles: the second angle is a+40=25+40=65a + 40 = 25 + 40 = 65, and the third angle is 9090.
  6. Check the solutions: Does 25+65+90=18025 + 65 + 90 = 180? Yes, 180=180180 = 180 \checkmark.
  7. Answer: The three angles measure 2525^\circ, 6565^\circ, and 9090^\circ.

Unlike problems where each angle is an explicit given number, this type of problem requires defining one angle in terms of another. Establishing all unknown angles through a single variable creates a two-step linear equation.

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Updated 2026-05-02

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