What are the slopes of line a and line b? look at the picture

we can mark points on the graph shown , check the image I have shared with this for the points .

Formula for slope =

So for Line A points are (1,3) and (0,-1)

So using t he formula slope is =

                  slope of line A =4

For Line B the points are  (0,4) and (3,-5)

So using t he formula slope is =

                  slope of line B = -3

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