Get date from week number in Google Sheets

=DATE(B9,1,1)-WEEKDAY(DATE(B9,1,1),3)+7*(WEEKDAY(DATE(B9,1,1),3)>3)+7*(A9-1)

is the least complicated formula I know which works for week numbers in Sweden (i.e. Monday first day of week, ISO rules for what is week 1).

Because of this definition (https://en.wikipedia.org/wiki/Week) the 4th of January must be used instead the 1st. The 4th of January is the first day which is always in the week 1.

=DATE(B1;1;4)+((A1-1)*7)-WEEKDAY(DATE(B1;1;4);3)

Short answer (A1==Week, B1==Year):

=DATE(B1;1;1)+((A1-1)*7)-WEEKDAY(DATE(B1;1;1);3)

Long answer:

DATE(<year>;1;1) // days since 1970 until the frist day of the year

plus

((<week number>-1)*7) // how many days into the year is this week

minus

WEEKDAY(DATE(<year>;1;1);3) // how many extra days from previous year in first week

PS:

This assumes monday as the first day of week you have to change the arguments for WEEKDAY to change it to sunday