The goal to proving identities is to transform one side into the other. We can only pick one side to transform while the other side stays the same the entire time. The general rule of thumb is to transform the more complicated side (though there may be exceptions to this guideline).
So I'll take the left hand side and try to turn it into 
One way we can do that is through the following steps:

Since we've shown that the left hand side transforms into the right hand side, this verifies the equation is an identity.
Answer:
(-3,-6) and (-3,2)
Step-by-step explanation:
A line with an undefined slope is vertical. In this case it must have x coordinates equal to -3
Answer:
25x - 45 = 5(5x - 9)
Step-by-step explanation:
Find the greatest common factor (GCF) of 25 and 45.
You can do this several ways, but one way is to list all the factors of both numbers and find the greatest common one:
Factors of 25: 1, 5, 25
Factors of 45: 1, 3, 5, 9, 15, 45
Therefore, 25 and 45 have 2 common factors: 1 and 5
So the greatest common factors is 5
25x - 45 = 5(ax - b)
To find the value of a, simply divide 25 by 5: 25 ÷ 5 = 5
To find the value of b, divide 45 by 5: 45 ÷ 5 = 9
25x - 45 = 5(5x - 9)
Answer:
a) for all values of x that are in the domains of f and g.
b) for all values of x that are in the domains of f and g.
c) for all values of x that are in the domains of f and g with g(x)≠0
Step-by-step explanation:
a) By definition (f+g)(x)=f(x)+g(x). Then x must be in the domain of f and g.
b) By definition (fg)(x)=f(x)g(x). Then x must be in the domain of f and g.
c) By definition (f/g)(x)=f(x)/g(x). Then x must be in the domain of f and g and g(x) must be different of 0.