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 y = 7√2
Step-by-step explanation:
We are given the side opposite the angle, and we want to find the hypotenuse. The relevant trig relation is ...
 Sin = Opposite/Hypotenuse
 sin(45°) = 7/y
 y = 7/sin(45°) = 7/(1/√2)
 y = 7√2
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Additional comment
In this 45°-45°-90° "special" right triangle, the two legs are the same length. Thus, ...
 x = 7