jika sudut antara A dan B 60° hitunglah nilai x vektor besar A 16 satuan B x satu

VEKTOR
• resultan

A = 16 satuan
B = x = __?
α = 60° → cos α = ½
|A + B| = 19 satuan

|A+B|² = |A|² + |B|² + 2 |A| |B| cos α
19² = 16² + x² + 2 • 16 • x • ½
361 = 256 + x² + 16x
0 = x² + 16x - 105
0 = (x - 5) (x + 21)
x = -21 [TM] atau x = 5 satuan ← jwb

nilai x = 5 satuan

cek :
|A+B|² = |A|² + |B|² + 2 |A| |B| cos α
|A+B|² = 16² + 5² + 2 • 16 • 5 • ½
|A+B|² = 256 + 25 + 80
19² = 361
cocok