I am really confused

How are sas and sss used to show that two triangles are congruent?

Look at the figure below: triangle abc is a right triangle with angle abc equal to 90 degrees. the length of ac is 5 units and the length of ab is 4 units. d is a point above c. triangle adc is a right triangle with angle dac equal to 90 degrees and dc parallel to ab. what is the length, in units, of segment cd?

Let f(x) = 5/x and g(x)=2x2+5x. what two numbers are not in the domain of f o g