Plane 1 contains points A(4,3,3) B(6,0,10) C(14,9,3) and plane 2 is given in standard form by -17x - 23y - 5z = -308.
1. Find cos(theta), where theta is an acute angle between the planes

Question

Plane 1 contains points A(4,3,3) B(6,0,10) C(14,9,3) and plane 2 is given in standard form by -17x - 23y - 5z = -308. 
1. Find cos(theta), where theta is an acute angle between the planes

anonymous · Answer

here's a pic of the question. the pi looking symbol is just a symbol they use and it doesn't mean anything other than a plane right?

anonymous · Answer

attachment

anonymous · Answer

k i don't understand why i am getting this wrong.
you find the equation of the first plane by finding vectors AB and AC, then take the cross product, which i got to be n=<-42,70,42>

anonymous · Answer

then just use the <-17,-23,5> from the second equation and plug into 
(a dot b) / mag of a * mag of b      = inverse cos to find theta

anonymous · Answer

which i got to be 114.52 but for some reason it keeps coming up wrong