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**Proove Vector Line Eqn is tangent to a sphere??**

Hi, iam hoping sum1 could explain to me how to proove that the line

r = -2i-j-11k + L(3i+4k) touches but doesnlt cut the sphere

Ab Value (r - (3i-j+4k)) = 5

I hav been able to find the postion vector of the point where they touch, which equals:

(7i-j+k)

however my first idea was that this position vecot would be perpendicular to the radius of the sphere and then use the dot product rule, ie if perpendicular and thus tangent, should = 0.......however this method doesnlt work.....any ideas or hints would be apprectiaed!!