1) Yes
2) COS of the angle times the distance to the target equal the distance to set scope to.
correct, theres a thing called a cosine angle indicator. they are expensive, I use an app on my phone with a level and set it on my barrel or scope and it gets me close.
if you have a smartphone there are ballistic apps to calculate your correction (strelok and shooter and more) that do it all. lots of online websites to play with also.
cosine is the ratio of the horizontal distance to the distance (line of sight) to the target. a percentage of the line of sight distance that is used for the "shoot to" distance which is always shorter than the line of sight dinstance. the steeper you look the smaller the cosine. so the shorter "shoot to"
distance is used.