Question 99201
f(x) and g(x) are functions - some rule of pairing, let's say we've got set A and want to assign every number from our set any different number, according to some pattern equation perhaps that could be y = x^2 = f(x) = x^2 value of function at any general point x. f(2) means value of function at point 2. if function is given by f(x) = 2x-5 then f(1)= 2*1-5= -3 and if g(x)=|-3-1| (you cannot substitute, because you do not have where - value of function g is constant and does not depend on value of x thus f(1)+g(2)=-3+|-3-1|
=(-3)+|-4|
=4-3
=1

{{{ graph( 300, 200, -10, 10, -10, 10, 2*x-5, 4) }}} 
that green line represents g(x) = see that for any x on x-axis(horizantal) there is same value on y-axis(vertical) function f(x) is different values of y depend on values of x