The ordered pair (3, –1) is a solution of which system?

In your equation, put 3 where x is, and -1 where y is. If you get a true statement, like -8 = -8, or 69 = 69, then (3, -1) is a solution. If you get a false statement, like 9 = 21 or 10 = 420, then (3, -1) is not a solution.

the answer is (4,3)

since the rule for r0, 90º is (-y,x) and it was already applied to form the image, all you have to do is reverse the answer using this formula.

not only in mathematics, scientific proof also are required in the other field of science. also maths proofs are of particular structure, containing steps and logics. so proving is like doing science, it is science. that's why it is important to prove. 

an inaccurate proof leads to errors, or stating results that are not accurate.  which wil mess the probelm up you dont want this