Look at attachment. How to write that graphs decrease simultaneously (at the same time).
Is it right to write X(arrow downwards)= (2;-2)
What do you mean by decrease simultaneously?
You can solve the two equations giving the co-ordinates that the graphs coincide? This can be done by solving equations simultaneously.
Another question might be to find the coodinates of the points where the graphs are decreasing at the same rate? This is a different problem and possibly more difficult.
I think you're being asked for the set of values of x for which each graph, regarded as a function of x, is decreasing. From the picture, one graph is decreasing for x < 0 and the other for -1 < x < 1. The intersection of these sets is the set of x such that -1 < x < 0, which is the open interval (-1,0).