math
posted by bhawani on .
given that vectors(p+2q) and (5p4q) are orthogonal,if vectors p and q are the unit vectors,find the dot product of vectors p and q?

we know that
(p+2q)•(5p4q) = 0
5p•p + 10p•q  4p•q  8q•q = 0
since p and q are unit vectors, we have
5 + 6p•q  8 = 0
p•q = 1/2