Question6

(x^2 + 10x + 21) / ( x^2 + 4x + 21)

The domain will be undefined for any "x" that makes the denominator = 0

But

x^2 + 4x  + 21  = 0      has no real 0's

So....this rational function is defined everywhere ....  (-inf, inf)

See the graph, here : https://www.desmos.com/calculator/t3utixb7ot

Oops....mis-read the denominator

x^2 +4x - 21    will have 0's  at

(x + 7) (x - 3)   = 0       set each factor to 0   and x = 3  or x = -7

So....the  domain  is  (-inf, -7) U (-7, 3) U (3, inf)

Thanks to hectictar and EP  for catching my error.....!!!!!