The price of an item has dropped to 63$ today yesterday it was 105$ find the percentage decrease

One expression below in undefined, and the other expression has a well defined value. which expression is undefined and explain why it has no value. which expression is defined? what is the value of that expression and how do you know? what is a different expression using a trig inverse function that is also undefined?

Can someone check if i did this right since i really want to make sure it’s correct. if you do you so much

∆red ≅ ∆ by rule will give brainiest if possible