a = 3i - 2j - 5k b = xi + yj + 3k c = 3i - 2j - 5k d = 3i + yj + xk Jika a tegak lurus dengan b dan c tegak lurus dengan d, maka nolau |a + b| = adalah...

a tegak lurus dengan b
--->>> axbx + ayby azbz = 0
--->>> 3(x) + -2(y) + -5(3) = 0
--->>> 3x -2y -15 = 0......(persamaan 1)

c tegak lurus d
--->>> CxDx + CyDy + CzDz = 0
--->>> 3(3) + -2(y) -5(x) = 0
--->>> 9 -2y -5x = 0.....(persamaan 2)

eliminasi
3x - 2y = 15
5x + 2y = 9
-------------------- +
8x = 24
x= 24/8 = 3

subtitusi
5x+2y = 9
5(3) + 2y = 9
2y= 9 - 15
y = -6/2 = -3

|a+b|^2 = |a|^2 + |b|^2 + 2ab
|a+b|^2 = 38 + 27 + 2(axbx +ayby +azbz)
|a+b|^2 = 65 + 2(3(3) + (-2)(-3) + (-5)(3))
|a+b|^2 = 65 +2(9+6-15)
|a+b|^2 = 65
|a+b| = ±√65

semoga membantu ;;))