U = pi - 2j + k v=2pi +pj -4k agar tegak lurus nilai p adlah

tegak lurus, maka
u . v = 0

(p,-2,1) . (2p,p,-4) = 0
2p² - 2p - 4 = 0
p² - p - 2 = 0
(p-2)(p+1) = 0
p = 2
p = -1