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... Vektor kecepatan rata-rata, v = Δr/Δt
t = 1 --> r1 = 3*1² i + 1³ j = 3 i + j
t = 3 --> r3 = 3*3² i + 3³ j = 27 i + 27 j
Δr = (27 i + 27 j) - (3 i + j) = 24 i + 26 j
Δt = 3 - 1 = 2
... Vektor kecepatan rata-rata, v = Δr/Δt = 12 i + 13 j
... Besar vektor kecp. rata-rata, │v│= √(12² + 13²) = √313 = 17,69
... Arah vektor kecp. rata-rata, tg θ = 13/12 --> θ = 47,29° (kuadran I)
b) r = 2/t i + (4 - 1/t² j
... Vektor kecepatan rata-rata, v = Δr/Δt
t = 1 --> r1 = 2 i + 3j
t = 3 --> r3 = (2/3) i + (35/9) j
Δr = (2/3 i + 35/9 j) - (2 i + 3j) = (-4/3) i + (8/9) j
Δt = 3 - 1 = 2
... Vektor kecepatan rata-rata, v = Δr/Δt = (-2/3) i + (4/9) j
... Besar vektor kecp. rata-rata, │v│= √((-2/3)² + (4/9)²) = 0,8
... Arah vektor kecp. rata-rata, tg θ = (4/9)/(-2/3) = -2/3 --> θ = 146,3° (kuadran II)