McGraw Hill Glencoe Geometry, 2012
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McGraw Hill Glencoe Geometry, 2012 View details
1. Geometric Mean
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Exercise 30 Page 542

Analyze what lengths you are given and use either the Geometric Mean (Altitude) Theorem or the Geometric Mean (Leg) Theorem.

x=sqrt(20)≈ 4.5
y= 2sqrt(5)3≈ 1.5
z= sqrt(2)3≈ 0.5

Practice makes perfect

We want to find the values of x, y, and z.

Notice that x and y are the legs of the given right triangle, and z is a partial segment of the hypotenuse divided by the altitude.

Finding z

Since we know the lengths of the altitude and of a partial segment of the hypotenuse, we will use the Geometric Mean (Altitude) Theorem to find the value of z.

We need to compare the theorem to the expressions in our figure. In our case, sqrt(2) is the length of the altitude, and z and 3sqrt(2) are the lengths of the partial segments of the hypotenuse. AD/CD = CD/DB ⇔ z/sqrt(2) = sqrt(2)/3sqrt(2) Now, we can find the value of z.
z/sqrt(2) = sqrt(2)/3sqrt(2)
Solve for z
z/sqrt(2) * sqrt(2) = sqrt(2)/3sqrt(2) * sqrt(2)
z = sqrt(2)/3sqrt(2) * sqrt(2)
z = sqrt(2) * sqrt(2)/3sqrt(2)
z = sqrt(2) * sqrt(2)/3 * sqrt(2)
z=sqrt(2)/3
Using a calculator, we can express z as about 0.5.

Finding x and y

Let's go back to the given figure.

Since we know the lengths of both partial segments of the hypotenuse, we will use the Geometric Mean (Leg) Theorem to find the values of x and y.

We will start by finding the value of x, which corresponds to CB on this figure. CB = sqrt(DB * AB) ⇕ x = sqrt(3sqrt(2)(3sqrt(2)+sqrt(2)/3)) To find the value of x, we will evaluate the right-hand side.
x=sqrt(3sqrt(2)(3sqrt(2)+sqrt(2)/3))
Evaluate right-hand side
x=sqrt((3sqrt(2))^2+3sqrt(2) * sqrt(2)/3)
x=sqrt(3^2(sqrt(2))^2+3sqrt(2) * sqrt(2)/3)
x=sqrt(9(2)+3sqrt(2) * sqrt(2)/3)
x=sqrt(9(2)+3sqrt(2)* sqrt(2)/3)
x=sqrt(9(2)+3* 2/3)
x=sqrt(18+6/3)
x=sqrt(18+2)
x=sqrt(20)
Using a calculator, we can rewrite x as about 4.5. Following the same reasoning, we can find y, which corresponds to AC. AC = sqrt(AD * AB) ⇕ y=sqrt(sqrt(2)/3 (3sqrt(2)+sqrt(2)/3)) Finally, we can evaluate the right-hand side to find the value of y.
y = sqrt(sqrt(2)/3(3sqrt(2)+sqrt(2)/3))
Evaluate right-hand side
y = sqrt(sqrt(2)/3 * 3sqrt(2)+(sqrt(2)/3)^2)
y = sqrt(sqrt(2)* 3sqrt(2)/3 +(sqrt(2)/3)^2)
y = sqrt(2 * 3/3 +(sqrt(2)/3)^2)
y = sqrt(2 * 3/3 +(sqrt(2))^2/3^2)
y = sqrt(2 * 3/3 +2/9)
y = sqrt(18/9 +2/9)
y = sqrt(20/9)
y = sqrt(20)/sqrt(9)
y = sqrt(4 * 5)/sqrt(9)
y = sqrt(4) * sqrt(5)/sqrt(9)
y = 2sqrt(5)/3
Using a calculator, we can rewrite y as about 1.5.