If ¯a,¯b are not perpendicular to each other and ¯rׯb=¯cׯb,¯r.¯a=0, then ¯r=
¯c −¯c.¯a¯c.¯b¯ a
¯c −¯c.¯a¯c.¯b¯ b
¯a,¯b≠0. ¯rׯb−¯cׯb =¯0⇒(¯r−¯c)ׯb=¯0∴ ¯r−¯c=λ¯b ⇒(¯r−¯c).¯a=λ¯b.¯a=λ=−¯c.¯a¯a.¯b ¯b