Question

find a if (a,4) and (2,5) are parallel vectors ?

Answer 1

a = 8/5

Answer 2

can u show the working ??? @Savvy

Answer 3

sure, since they are parallel vectors(NOTE: they are to be specified as position vectors) hence the co-ordinates of the vectors should be proportional....
5/4 = 2/a

Answer 4

or else you could find a unit vector in the direction of the 2nd vector and multiply it by the required magnitude which can be deciphered by the y co-ordinate of the 1st vector...