Nice job, irspow! I like it!

slope is negative reciprocal of other slope.

And then you have to mentally know the... Uh oh,

there is one mistake, though, minor typo.

x is y and y is x for the final answer.

So it is (10.29,6.68) for C.

So anyway I was going to say you mentally have to see which way

the 90 degrees points the vector up and left, hence the subtract sign

for the cosine for x value, and the plus for sine, and they have to

be different signs because slope is negative now.