Slide #1
8.1 Geometric Mean and Pythagorean Theorem Geometry
Objectives/Assignment Use Pythagorean theorem to solve problems Use Geometric Mean and Pythagorean Theorem to solve real-life problems
Geometric Mean The geometric mean of two positive numbers a and b is the positive number x such that a x If you solve this proportion for x, you find that x = √a ∙ b which is a positive number. = x b
Book Example Pg 397
Geometric Mean Example For example, the geometric mean of 8 and 18 is 12, because 8 12 = 12 18 and also because x = √8 ∙ 18 = x = √144 = 12
Practice “Geometric Mean”
Geometric mean PAPER SIZES. International standard paper sizes are commonly used all over the world. The various sizes all have the same width-to-length ratios. Two sizes of paper are shown, called A4 and A3. The distance labeled x is the geometric mean of 210 mm and 420 mm. Find the value of x.
Write proportion 210 x = x 420 X2 = 210 ∙ 420 X = √210 ∙ 420 X = 297mm Solution: 210 x Write proportion = x 420 X2 = 210 ∙ 420 X = √210 ∙ 420 X = 297mm Cross product property Simplify
Find the positive square root. EXAMPLE 1 Find the length of a hypotenuse Find the length of the hypotenuse of the right triangle. (hypotenuse)2 = (leg)2 + (leg)2 Pythagorean Theorem x2 = 62 + 82 Substitute. x2 = 36 + 64 Square. x2 = 100 Add. x = 10 Find the positive square root.
GUIDED PRACTICE for Example 1 1. Find the unknown side length of the right triangle. Write your answer in simplest radical form. ANSWER 4
GUIDED PRACTICE for Example 1 Find the unknown side length of the right triangle. 2. 13 ANSWER
X = 3.2 Y = X + 5 Y = 3.2 + 5 Y = 8.2
5.7²+ 8² = x² 32.49 + 64 = x² 96.49 = x² X = 9.8 Y² = 32 Y = 5.7
x 4 4.5²+ 5² = y² 20 + 25 = y² 45 = y² X = 6.7 x² = 20 x = 4.5
x² = 18 x = 4.2 6²+ 4.2² = y² 36 + 18 = y² 54 = y² X = 7.3
x²+ 5² = 9² x² + 25 = 81 x² = 81-25 X² = 56 X = 7.5
2²+ 2² = x² 4 + 4 = x² x² = 8 X = 2.8
30²+ 16² = x² 900+256 = x² x² = 1156 X = 34
x+ 60² = 65² x² +3600 = 4225 x² = 4225-3600 x² = 625 X = 25
14² + 48² = 50² 50² + 75² = 85² 15² + 36² = 39² 45² + 60² = 80² ?