The website wolframalpha.com is very helpful for this. Go there and just type 'july 17 1975' into the search box, and it will give you the correct answer.
According to wolframalpha.com, it was a Thursday.
Monday
July 17, 1963 fell on a Wednesday.
Tuesday
Monday
Sunday - Source: http://scphillips.com/units/dayform.html
25 July 1975 was a Friday.
December 17 1975 was on a Wednesday.
July 11, 1975 fell on a Friday.
July 9, 1975 fell on a Wednesday.
July 16, 1975 fell on a Wednesday.
July 10, 1975 fell on a Thursday.
July 24, 1975 fell on a Thursday.
July 12, 1975 was a Saturday.
17 September 1975 was a Wednesday.
May 17, 1975 fell on a Saturday.
October 17, 1975 fell on a Friday.
February 17, 1975 fell on a Monday.