Step-by-step explanation:
A function is continuous at x is
Limit as x approaches c= f(c).
Step 1: Find f(4).
4 is defined for 2x-1 so plug in. 4 for x.
[tex]2(4) - 1 = 7[/tex]
Note that what we just calculated was not only f(4) but also the left sided limit of f(x).
Step 2: Make sure the left sided and right sided limit are equal to 7.
[tex]a + 5x = 7[/tex]
Plug in 4 for x
[tex]a + 5(4) = 7[/tex]
[tex]a = - 13[/tex]
