Question

Tolong nomer 7 dan 8 jawabannya kalau bisa difoto n pakai caranya buat belajar ulangan soalnya

Answer 1

7) u tegak lurus v maka
u.v = 0
=> 5√8 + x√2 = 0
=> x√2 = -5√8
=> x = -5√8 / √2 = -5√4 = -10

8) a = (3 -4 5) => |a| = √(3^2 + (-4)^2 + 5^2)
= √(9 + 16 + 25) = √50 = 5√2
b = (8 6 x) => |b| = √(8^2 + 6^2 + x^2)
= √(64 + 36 + x^2) = √(100 + x^2)

a.b = |a| . |b| cos 120°
=> 3(8) + -4(6) + 5(x) = 5√2 . √(100 + x^2) . -1/2
=> 24 - 24 + 5x = -5/2 . √(200 + 2x^2)
=> 5x . 2/-5 = √(200 + 2x^2)
=> -2x = √(200 + 2x^2)
=> 4x^2 = 200 + 2x^2
=> 2x^2 = 200
=> x^2 = 100
=> x = ± 10
x = 10 atau x = -10