Math Problem Statement

In the following diagram of one section of a bridge truss, CD is the perpendicular bisector of AB. If BD is 70 feet and CD is 25 feet, what is the length of AB?

Solution

We are given a diagram where CD\overline{CD} is the perpendicular bisector of AB\overline{AB}, and we know the following:

  • BD=70feetBD = 70 \, \text{feet}
  • CD=25feetCD = 25 \, \text{feet}

Since CDCD is the perpendicular bisector of ABAB, it means that CC is the midpoint of ABAB, and BCD\triangle BCD is a right triangle with a right angle at CC.

To find the length of ABAB, we can use the Pythagorean theorem on BCD\triangle BCD. The theorem states that:

BD2=BC2+CD2BD^2 = BC^2 + CD^2

We are looking for the length of ABAB, which is 2×BC2 \times BC because CC is the midpoint of ABAB. Let's first solve for BCBC using the Pythagorean theorem:

BD2=BC2+CD2BD^2 = BC^2 + CD^2 702=BC2+25270^2 = BC^2 + 25^2 4900=BC2+6254900 = BC^2 + 625 BC2=4900625=4275BC^2 = 4900 - 625 = 4275 BC=4275BC = \sqrt{4275}

Now, I'll calculate the value of BCBC.The length of BCBC is approximately 65.38 feet. Since ABAB is twice the length of BCBC (because CC is the midpoint), the length of ABAB is:

AB=2×BC=2×65.38=130.77feetAB = 2 \times BC = 2 \times 65.38 = 130.77 \, \text{feet}

Thus, the length of ABAB is approximately 130.77 feet.

Would you like more details or have any questions?

Here are 5 related questions to expand your understanding:

  1. What is the significance of a perpendicular bisector in geometry?
  2. How does the Pythagorean theorem apply to right triangles in construction problems?
  3. How would the problem change if CD\overline{CD} was not a perpendicular bisector?
  4. What other methods could be used to find the length of ABAB in a different context?
  5. How would the trigonometric functions apply if the angles in the triangle were known?

Tip: Always double-check the geometric properties of a figure when solving word problems, especially whether lines are perpendicular or bisecting.

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Math Problem Analysis

Mathematical Concepts

Geometry
Right Triangle Properties
Pythagorean Theorem

Formulas

Pythagorean theorem: a^2 + b^2 = c^2

Theorems

Properties of Perpendicular Bisectors

Suitable Grade Level

High School