9514 1404 393
(d) 6√3
Step-by-step explanation:
There are several ways to work multiple-choice problems. One of the simplest is to choose the only answer that makes any sense. Here, that is 6√3.
y is the hypotenuse of the medium-sized right triangle, so will be longer than that triangle's longest leg. y > 9
The only answer choice that meets this requirement is ...
y = 6√3
__
In this geometry, all of the right triangles are similar. This means corresponding sides have the same ratio. For y, we're interested in the ratio of long leg to hypotenuse.
long leg/hypotenuse = y/(9+3) = 9/y
y² = 9(9+3) = 9·4·3
y = 3·2·√3 . . . . . . take the square root
y = 6√3
__
Additional comments
You may notice that y is the root of the product of the longer hypotenuse segment (9) and the whole hypotenuse (9+3 = 12). We can say that y is the "geometric mean" of these segment lengths. Similarly (pun only partially intended), x will be the root of the product of the short segment (3) and the whole hypotenuse (12)
x = √(3·12) = 6
This is another "geometric mean" relation.
Further, the altitude will be the geometric mean of the two segments of the hypotenuse:
h = √(9·3) = 3√3
A way to summarize all of these relations is to say that the legs of the right triangle that are not the hypotenuse are equal to the geometric mean of the segments of the hypotenuse that the leg intercepts.
x = √(3·12)
y = √(9·12)
h = √(3·9)
