Aim: What is the Law of Cosines?
Homework # Do Now: In triangle ABC, side a=8, measure of angle A = 30o and measure of angle C = 55o. Find side b to the nearest tenth of an integer.
Mar 27­2:16 PM
Law of Cosines: The square of the measure of one side of a triangle is equal to the sum of the squares of the measures of the other two sides minus twice the product of the measures of these two sides and the cosine of the angle between them.
Apr 19­10:18 PM
1
Examples:
1. In triangle ABC, if a = 4,
c = 6, and cosB = 1/16, find b.
2. In triangle ABC, a = 5,
b = 7, and c= 10. a. Find CosB
b. Find angle B to the nearest degree.
Mar 27­2:20 PM
3. Find the length of the longer diagonal of a parallelogram if the lengths of two adjacent sides are 6 and 10 and the measure of the angle included between them is 1200.
Mar 27­2:21 PM
2
4. In triangle ABC, the measures of the sides are 3,5 and 7. Find, to the nearest degree, the largest angle of the triangle.
Apr 19­10:28 PM
Example 5: In a parallelogram, the adjacent sides measure 40 cm and 22 cm. If the larger angle of the parallelogram measure 1160, find the length of the larger diagonal, to the nearest integer. Apr 19­10:30 PM
3
Extra Practice
Answer
Apr 25­10:59 PM
Extra Practice
Apr 25­10:59 PM
4
May 2­7:45 PM
5