SAT II Math II : Law of Sines

Study concepts, example questions & explanations for SAT II Math II

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Example Questions

Example Question #461 : Sat Subject Test In Math Ii

Find the measure of angle \(\displaystyle A\).

2

Possible Answers:

\(\displaystyle 109.73\)

\(\displaystyle 70.27\)

\(\displaystyle 61.20\)

\(\displaystyle 78.61\)

Correct answer:

\(\displaystyle 70.27\)

Explanation:

2

Start by using the Law of Sines to find the measure of angle \(\displaystyle B\).

\(\displaystyle \frac{8}{\sin 39}=\frac{12}{\sin B}\)

\(\displaystyle 12\sin 39=8\sin B\)

\(\displaystyle \sin B=0.94398\)

\(\displaystyle B=70.73^{\circ}\)

Since the angles of a triangle must add up to \(\displaystyle 180\),

\(\displaystyle 39+70.73+A=180\)

\(\displaystyle A=70.27^{\circ}\)

 

 

Example Question #462 : Sat Subject Test In Math Ii

In \(\displaystyle \bigtriangleup ABC\)

\(\displaystyle AB = 23\)

\(\displaystyle BC = 34\)

\(\displaystyle \angle C =65 ^{\circ }\)

Evaluate \(\displaystyle m \angle A\) (nearest degree)

Possible Answers:

Cannot be determined

\(\displaystyle 77^{\circ }\)

\(\displaystyle 41^{\circ }\)

\(\displaystyle 38^{\circ }\)

\(\displaystyle 74^{\circ }\)

Correct answer:

Cannot be determined

Explanation:

By the Law of Sines, if \(\displaystyle a\) and \(\displaystyle b\) are the lengths of two sides of a triangle, and \(\displaystyle \alpha\) and \(\displaystyle \beta\) the measures of their respective opposite angles, 

\(\displaystyle \frac{\sin \alpha }{a} = \frac{\sin \beta }{b}\)

\(\displaystyle \angle A\) and \(\displaystyle \angle C\) are opposite sides \(\displaystyle \overline{BC}\) and \(\displaystyle \overline{AB}\), so, setting \(\displaystyle \alpha = m \angle A\)\(\displaystyle \beta = m\angle C = 65^{\circ }\)\(\displaystyle a = BC = 34\), and \(\displaystyle b = AB = 23\):

\(\displaystyle \frac{\sin \alpha }{34} = \frac{\sin 65^{\circ } }{23}\)

\(\displaystyle \frac{\sin \alpha }{34}\cdot 34 = \frac{\sin 65^{\circ } }{23} \cdot 34\)

\(\displaystyle \sin \alpha \approx \frac{0.9063 }{23} \cdot 34 \approx 1.3398\)

However, the range of the sine function is \(\displaystyle [-1, 1]\), so there is no value of \(\displaystyle \alpha\) for which this is true. Therefore, this triangle cannot exist.

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