Use the Law of Cosines, a2=b2+c2−2bc⋅cosA , to find the value of angle A in a right triangle, where a=7 , b=24 , and c=25 .(1 point)

Responses

89.9 degrees
89.9 degrees

25.1 degrees
25.1 degrees

16.3 degrees
16.3 degrees

73.6 degrees
73.6 degrees

1 answer

To find the angle \( A \) in the triangle using the Law of Cosines, we can rearrange the Law of Cosines formula:

\[ a^2 = b^2 + c^2 - 2bc \cdot \cos A \]

From rearranging this formula, we can solve for \( \cos A \):

\[ \cos A = \frac{b^2 + c^2 - a^2}{2bc} \]

Given:

  • \( a = 7 \)
  • \( b = 24 \)
  • \( c = 25 \)

Now we can calculate:

  1. Calculate \( b^2 \) and \( c^2 \):

\[ b^2 = 24^2 = 576 \] \[ c^2 = 25^2 = 625 \]

  1. Calculate \( a^2 \):

\[ a^2 = 7^2 = 49 \]

  1. Substitute these values into the formula for \( \cos A \):

\[ \cos A = \frac{576 + 625 - 49}{2 \cdot 24 \cdot 25} \] \[ \cos A = \frac{1152}{1200} \] \[ \cos A = 0.96 \]

  1. Now calculate \( A \) by taking the arccosine:

\[ A = \cos^{-1}(0.96) \]

Using a calculator:

\[ A \approx 15.9 \text{ degrees} \]

This is close to the option of \( 16.3 \) degrees. Thus, the angle \( A \) is approximately \( 16.3 \) degrees.

The correct response is:

16.3 degrees