Question

WILL MAKE BRAINLIEST!!! A triangular section of a lawn will be converted to river rock instead of grass. Maurice insists that the only way to find a missing side length is to use the Law of Cosines. Johanna exclaims, that only the Law of Sines will be useful. Describe a scenario where Maurice is correct, a scenario where Johanna is correct, and a scenario where both laws are able to be used. Use complete sentences and example measurements when necessary.

Answer 1

Let's consider the triangle ABC shown in the first diagram below. We name the sides with small letters: a, b, and c. We name the angles by the capital letters A, B, and C. Side a pairs with angle A° which are opposite each other. The same with side b and angle B° and side c and angle C°.

We can use the cosine rule when we know the length of two sides and the angle opposite the side that is unknown. For example, referring to the second diagram, we know the length of side a and side b and we are looking for the length of side c. We also know the angle that is located on the opposite of side c, then to solve this we can use the cosine rule

c² = a² + b² - 2ab(cos(C°))

The third diagram shows a scenario when sine rule can be used. Say we need the length of the side c. We know the length of side a, the size of angle A° and angle C° then we can use the sine rule

$\frac{c}{sin(C)} = \frac{a}{sin(A)}$

We can also use sine rule if we know length of side b and the size of angle B° instead of side a and angle A°