Question

Difficulty: HardLines and Angles

In a geometric diagram, angle α\alpha and angle β\beta are complementary. Furthermore, angle β\beta and angle γ\gamma are supplementary. If the measure of angle α\alpha is represented by the expression (2x−5)∘(2x - 5)^\circ and the measure of angle γ\gamma is represented by (5x−2)∘(5x - 2)^\circ, what is the measure of angle β\beta?

  1. 37∘37^\circAnswer
  2. B
    97∘97^\circ
  3. C
    135∘135^\circ
  4. D
    153∘153^\circ

Answer

37∘37^\circ
The correct answer is found by recognizing that angle β\beta can be expressed in two ways: 90∘−α90^\circ - \alpha and 180∘−γ180^\circ - \gamma. Setting 90−(2x−5)90 - (2x - 5) equal to 180−(5x−2)180 - (5x - 2) allows us to solve for x=29x = 29. Substituting xx back into the first expression yields 95−2(29)=37∘95 - 2(29) = 37^\circ.

Step-by-Step Solution

1
Express angle beta in terms of x using the complementary relationship.
β=90−(2x−5)=95−2x\beta = 90 - (2x - 5) = 95 - 2x
Since alpha and beta are complementary, their sum is 90 degrees.
2
Express angle beta in terms of x using the supplementary relationship.
β=180−(5x−2)=182−5x\beta = 180 - (5x - 2) = 182 - 5x
Since beta and gamma are supplementary, their sum is 180 degrees.
3
Set the two expressions for beta equal to each other and solve for x.
95−2x=182−5x⇒3x=87⇒x=2995 - 2x = 182 - 5x \Rightarrow 3x = 87 \Rightarrow x = 29
Both expressions represent the same angle, so they must be algebraically equivalent.
4
Substitute the value of x back into either expression to find the measure of angle beta.
β=95−2(29)=95−58=37∘\beta = 95 - 2(29) = 95 - 58 = 37^\circ
This provides the final numerical measure of the target angle.

Key Concept

Algebraic application of complementary and supplementary angle relationships
Estimated Time:2m 0s
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