Answer:
You need to find the numbers which makes your function undefined and then subtract them from the Real numbers set for example if you had
[tex] \sqrt{x} [/tex]
function you need to make sure that the x won't be negative number ( even roots of negative numbers are undefined ) thus the domain would be [0,+∞)
for another example
[tex] \frac{x - 5}{x - 6} [/tex]
in this function u need to make sure that denominator won't be 0 so you need to solve this equation x-6=0 which would be x=6 thus the domain would be R-6
I hope this practice would be useful, if you have any specific functions that u needed to find the domain please comment it below thanks!