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Diketahui a , b dan c vektor pada bidang, a + b + c = 0 , b = i − 2 j ​ , b ⊥ c dan α adalah sudut yang dibentuk oleh a dan c . Jika luas segitiga yang dibentuk oleh titik ujung vektor-vekto , dan adalah 5 satuan luas, maka cosinus adalah....

Diketahui , dan  vektor pada bidang,  dan adalah sudut yang dibentuk oleh  dan . Jika luas segitiga yang dibentuk oleh titik ujung vektor-vekto straight a with rightwards arrow on top,straight b with rightwards arrow on top dan straight c with rightwards arrow on top adalah 5 satuan luas, maka cosinus straight alpha adalah....

  1. negative 2 over 5 square root of 5

  2. negative 1 fifth square root of 5

  3. 1 fifth square root of 5

  4. 1 half square root of 5

  5. 2 over 5 square root of 5

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* maka ** maka luas segitiganya= *** Diketahui: maka Terakhir

* straight b with rightwards arrow on top perpendicular straight c with rightwards arrow on top maka straight b with rightwards arrow on top times straight c with rightwards arrow on top equals 0 rightwards double arrow open parentheses table row 1 row cell negative 2 end cell end table close parentheses times open parentheses table row cell straight c subscript 1 end cell row cell straight c subscript 2 end cell end table close parentheses equals straight c subscript 1 minus 2 straight c subscript 2 equals 0 rightwards double arrow straight c subscript 1 equals 2 straight c subscript 2

** straight b with rightwards arrow on top perpendicular straight c with rightwards arrow on top maka luas segitiganya=

1 half open vertical bar straight b with rightwards arrow on top close vertical bar open vertical bar straight c with rightwards arrow on top close vertical bar equals 5 1 half square root of 1 plus 4 end root times open vertical bar straight c with rightwards arrow on top close vertical bar equals 5 square root of 5 times open vertical bar straight c with rightwards arrow on top close vertical bar equals 10 open vertical bar straight c with rightwards arrow on top close vertical bar equals 2 square root of 5

*** open vertical bar straight c with rightwards arrow on top close vertical bar equals square root of straight c subscript 1 squared plus straight c subscript 2 squared end root equals 2 square root of 5 square root of 4 straight c subscript 1 squared plus straight c subscript 2 squared end root equals 2 square root of 5 straight c subscript 2 square root of 5 equals 2 square root of 5 straight c subscript 2 equals 2 straight c subscript 1 equals 4

Diketahui: straight a with rightwards arrow on top plus straight b with rightwards arrow on top plus straight c with rightwards arrow on top equals 0  maka straight a with rightwards arrow on top plus straight b with rightwards arrow on top equals negative straight c with rightwards arrow on top rightwards arrow open parentheses table row cell straight a subscript 1 end cell row cell straight a subscript 2 end cell end table close parentheses plus open parentheses table row 1 row cell negative 2 end cell end table close parentheses equals negative open parentheses table row 4 row 2 end table close parentheses rightwards arrow open parentheses table row cell straight a subscript 1 end cell row cell straight a subscript 2 end cell end table close parentheses equals open parentheses table row cell negative 5 end cell row 0 end table close parentheses
Terakhir  cos space straight alpha equals fraction numerator straight a with rightwards arrow on top times straight c with rightwards arrow on top over denominator open vertical bar straight a with rightwards arrow on top close vertical bar open vertical bar straight c with rightwards arrow on top close vertical bar end fraction equals fraction numerator open parentheses table row cell negative 5 end cell row 4 end table close parentheses times open parentheses table row 4 row 2 end table close parentheses over denominator 5 times 2 square root of 5 end fraction equals fraction numerator negative 20 over denominator 10 square root of 5 end fraction equals negative 2 over 5 square root of 5

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Diketahui a → , b → , dan c . Vektor dalam dimensi 3. Jika sudut antara a dan b adalah 6 0 ∘ , a ⊥ ( b − 2 c ) , dan ∣ ∣ ​ b ∣ ∣ ​ = 3 ∣ ∣ ​ c ∣ ∣ ​ maka cosinus sudut antara a → dan adalah....

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