Someone please explain these!

The angle between two planes is defined as the angle between their normals. Determine the angle theta between 0 and 90 degrees between the given planes.

a) 2x+3y-z+9 = 0 and x+2y+4 = 0

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If the positive z-axiz points up, show that the line x=0, y=t, z=2t is parallel to and below the plane 2x-10y+5z-1 = 0.

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Find an equation for the set of points P(x,y,z) that are equidistant from the points A(1,2,3) and B(4,0,1)

3 answers

what is the answer to 2+3+6+7+9+n=100?

n=73