9514 1404 393
Answer:
(d) 21 inches
Explanation:
The missing altitude of the smaller isosceles triangle can be found from the Pythagorean theorem as ...
h1 = √(10^2 -8^2) = √36 = 6
Likewise, the missing altitude of the larger triangle is ...
h2 = √(17^2 -8^2) = √225 = 15
The length of the other diagonal is the sum of these two triangle altitudes:
diagonal length = 6 +15 = 21 . . . inches
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Additional comment
You may recognize the Pythagorean triples involved as being ...
(3, 4, 5)×2 and (8, 15, 17)