Let a and b be sets. let f : a ? b. recall that f^1 : p(a) ? p(b) is defined by f^1(s) = {f(x)| x ? s}.
(a) prove that if f is an injection, then f^1 is an injection.
(b) prove that if f^1 is an injection, then f is an injection.
(f^1) is just symbol. i can not type actual symbol, so i just change that.
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( f ) orignal symbol is like that. arrow is above f

Answer this two poles, ab and ed, are fixed to the ground with the of ropes ac and ec, as shown: two right triangles abc and edc have a common vertex c. angle abc and edc are right angles. ab is labeled 13 feet, ac is labeled 15 feet, ec is labeled 10 feet, and ed is labeled 4 feet.what is the approximate distance, in feet, between the two poles? 11.14 feet16.65 feet14.35 feet15.59 feet