It is known that the a vector is equal to (1, 5) and the b vector is equal to (-3, 2), then the number of positive photographs in the a and b directions

The angle between vector a and vector b is w, then the projection of vector a on vector b is: |a|cosw

Because:

a *b=|a|×|b|×cosw, |b|=√13, a*b=-3+10=7

Then: |a|cosa=[a*b]/[| b|]=7/√13