Answer:
(7√6)/2
Step-by-step explanation:
The side ratios in these special triangles are ...
30°-60°-90° triangle: 1 : √3 : 2
45°-45°-90° triangle: 1 : 1 : √2
This tells you the length of the horizontal line is 7√3, and the value of x is ...
(7√3)/√2 = (7√6)/2
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Additional comment
Call the length of the horizontal line "y". Then the given ratios tell you ...
7 : y = 1 : √3 ⇒ y/7 = √3/1 ⇒ y = 7√3
and
x : y = 1 : √2 ⇒ x/y = 1/√2 ⇒ x = y/√2
When we rationalize the denominator, we get ...
x = (y√2)/2 = ((7√3)√2)/2 = (7√6)/2
