Share cara paling cepatnya dong, buat ujian soalnya... UTUL UGM 2017 no. 11

w tegak lurus u dan v, maka
u x v = w
((u2.v3 - u3.v2), (u3.v1 - u1.v3), (u1,v2 - u2.v1)) = w
((1(-1) - 2(-1)), (2(-1) - a.(-1)), (a(-1) - 1(-1)) = w
w = (1, a - 2, -a + 1)

|w| = 3
akar(1² + (a - 2)² + (-a + 1)²) = 3
1² + (a - 2)² + (-a + 1)² = 9
1 + a² - 4a + 4 + a² - 2a + 1 = 9
2a² - 6a + 6 = 9
2a² - 6a - 3 = 0

a = 2, b = -6, c = -3

Jumlah nilai a yg mungkin
= -b/a
= -(-6)/2
= 3

Jawaban C

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