Find the measure of [tex]\(\angle J\)[/tex], the smallest angle in a triangle with sides measuring 11, 13, and 19. Round to the nearest whole degree.

A. [tex]\(30^\circ\)[/tex]
B. [tex]\(34^\circ\)[/tex]
C. [tex]\(42^\circ\)[/tex]
D. [tex]\(47^\circ\)[/tex]

Law of cosines: [tex]\(a^2 = b^2 + c^2 - 2bc \cos(A)\)[/tex]



Answer :

To find the measure of angle [tex]\( \angle J \)[/tex] in a triangle with sides measuring [tex]\( 11 \)[/tex], [tex]\( 13 \)[/tex], and [tex]\( 19 \)[/tex], we can use the Law of Cosines, which states:
[tex]\[ a^2 = b^2 + c^2 - 2bc \cos(A) \][/tex]
In this context, let's name the sides of the triangle as follows:
- [tex]\( a = 11 \)[/tex] (the side opposite angle [tex]\( J \)[/tex])
- [tex]\( b = 13 \)[/tex]
- [tex]\( c = 19 \)[/tex]

We need to find the measure of [tex]\( \angle J \)[/tex]. By rearranging the Law of Cosines formula, we have:
[tex]\[ \cos(J) = \frac{b^2 + c^2 - a^2}{2bc} \][/tex]

Substitute the known values into the formula:
[tex]\[ \cos(J) = \frac{13^2 + 19^2 - 11^2}{2 \cdot 13 \cdot 19} \][/tex]

Calculate the squares of the sides:
[tex]\[ 13^2 = 169, \quad 19^2 = 361, \quad 11^2 = 121 \][/tex]

Substitute these values into the equation:
[tex]\[ \cos(J) = \frac{169 + 361 - 121}{2 \cdot 13 \cdot 19} \][/tex]

Simplify the numerator:
[tex]\[ 169 + 361 - 121 = 409 \][/tex]

Substitute back into the equation:
[tex]\[ \cos(J) = \frac{409}{2 \cdot 13 \cdot 19} \][/tex]
[tex]\[ \cos(J) = \frac{409}{494} \][/tex]

Calculate the value:
[tex]\[ \cos(J) \approx 0.82834 \][/tex]

To find [tex]\( \angle J \)[/tex], take the arccosine (inverse cosine) of this value:
[tex]\[ J \approx \arccos(0.82834) \][/tex]

Convert this angle from radians to degrees:
[tex]\[ J \approx 34.11 \text{ degrees} \][/tex]

When rounding to the nearest whole degree, we find:
[tex]\[ J \approx 34^\circ \][/tex]

Thus, the measure of [tex]\( \angle J \)[/tex], rounded to the nearest whole degree, is:
[tex]\[ \boxed{34^\circ} \][/tex]

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