How do I find the angle between vectors #<3, 0># and #<5, 5>#?

1 Answer
Sep 27, 2014

Let's begin by naming our vectors.

v#=<3,0>#
w#=<5,5>#

Dot product #-> v*w#

Angle between formula #->cos (theta)=(v*w)/(||v||*||w||)#

Solve for #theta#

#cos^-1(cos (theta))=cos^-1((v*w)/(||v||*||w||))#

#theta=cos^-1((v*w)/(||v||*||w||))#

Begin by finding the dot product of vectors #v and w# by adding the products of the horizontal and vertical components.

#theta=cos^-1(((3)(5)+(0)(5))/(||v||*||w||))#

#theta=cos^-1((15+0)/(||v||*||w||))#

Now find the magnitudes of both vectors

#theta=cos^-1((15)/(sqrt(9+0)*sqrt(25+25)))#

#theta=cos^-1((15)/(sqrt(9)*sqrt(50)))#

#theta=cos^-1((15)/(sqrt(3*3*5*5*2)))#

#theta=cos^-1((15)/(15sqrt(2)))#

#theta=cos^-1((1)/(sqrt(2)))#

#theta=pi/4#