If `veca=2veci+3vecj-4veck and vecb =5veci+2vecj+4veck`, find the angle between `veca and vecb`.

Explanation

We have `veca.vecb=ab costheta`
or `costheta= (veca.vecb)/(ab)`
where `theta` is the angle between `veca and vecb`
Now `veca.veb=a_xb_x+a_yb_y+a_zb^z`
`=2xx4+3xx3+4xx2=25`
Also, `veca=sqrt(a_x^2+a_y^2+a_z^2)
`=sqrt(4+9+16)= sqrt29`
and ` b= sqrt(b_x^2+b_u^2+b_z^2= sqrt(16+9+4)= sqrt(16+9+4)=sqrt29`
Thrus, `costheta = 25/29`
`or, `theta= cos^-1 (25/29)`.