Best anwser gets brain select all that apply​

Which best explains why this triangle is or is not a right triangle ?

Def rotates 90 clockwise about point a to create d’ e’ f’. therefore, which equation must be true ?

Sandy is upgrading her internet service. fast internet charges $20 for installation and $52.45 per month. quick internet has free installation but charges $57.45 per month. part 1 out of 2 complete the equation that can be used to find the number of months after which the internet service would cost the same. use the variable x to represent the number of months of internet service purchased.