Solution:

( 1)x？ -3x-4=0

Solution: x=4 or x=- 1.

The solution set of equation ∴ is {- 1, 4}

(2)4x+3=0

So x=-3/4.

So the set is {-3/4}

(3) Because the set consists of 1, 4,9,16,25.

So the set can be expressed as: {1, 4,9,16,25}

(4) Because the set consists of all positive odd numbers.

So the set can be expressed as: {x|x=2k- 1, k∈N+}

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