diketahui vektor a=2i - 6j - 3k b=xi + 2j - 4k panjang proyeksi vektor a pada b adalah 4/3 maka x ?

panjang proyeksi vektor = ( a×b )/|b|
4/3 = ((2,-6,-3)×(x,2,-4))/ akar (x^2+2^2+(-4)^2)
4/3 = (2x+(-12)+12)/akar (x^2+4+16)
4/3 = 2x/akar (x^2+20)
4/3 × akar (x^2+20) = 2x
akar (x^2+20) = 2x / 4/3
akar (x^2+20) = 2x × 3/4
akar (x^2+20) = 6x/4
x^2+20 = (6x/4)^2
x^2+20 = 36x^2/16
36x^2 = 16×(x^2+20)
36x^2 = 16x^2+320
36x^2-16x^2=320
20x^2 = 320
x^2 = 320/20 = 16
x = akar (16)
x = 4
jadi nilai x = 4