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Jika vektor satuan dari a = 6 i + s j ​ adalah , maka st = ....

Jika vektor satuan dari  adalah begin mathsize 14px style e subscript a with rightwards arrow on top end subscript equals t i with rightwards arrow on top minus 4 over 5 j with rightwards arrow on top end style, maka st = ....

  1. begin mathsize 14px style 40 over 3 end style  

  2. begin mathsize 14px style negative 40 over 3 end style  

  3. 8

  4. begin mathsize 14px style negative 24 over 5 end style  

  5. begin mathsize 14px style 24 over 5 end style  

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Pembahasan

Perhatikan bahwa adalah vektor satuan. Sehingga Sehingga Karena adalah vektor satuan, maka Jika diperhatikan, tidak mungkin bernilai negatif. Sehingga t tidak mungkin bernilai negatif, maka . Sehingga Kemudian perhatikan bahwa Ruas kiri bernilai negatif, sehingga ruas kanan juga harus bernilai negatif. Hal ini terpenuhi jika s negatif, maka s = -8. Maka

Perhatikan bahwa begin mathsize 14px style e subscript a with rightwards arrow on top end subscript equals t i with rightwards arrow on top minus 4 over 5 j with rightwards arrow on top end style adalah vektor satuan. Sehingga

table attributes columnalign right center left columnspacing 0px end attributes row cell size 14px e subscript size 14px a with size 14px rightwards arrow on top end subscript end cell size 14px equals cell fraction numerator size 14px a with size 14px rightwards arrow on top over denominator begin mathsize 14px style vertical line a with rightwards arrow on top vertical line end style end fraction end cell row cell size 14px t size 14px i with size 14px rightwards arrow on top size 14px minus size 14px 4 over size 14px 5 size 14px j with size 14px rightwards arrow on top end cell size 14px equals cell fraction numerator size 14px 6 size 14px i with size 14px rightwards arrow on top size 14px plus size 14px s size 14px j with size 14px rightwards arrow on top over denominator square root of size 14px 6 to the power of size 14px 2 size 14px plus size 14px s to the power of size 14px 2 end root end fraction end cell row cell size 14px t size 14px i with size 14px rightwards arrow on top size 14px minus size 14px 4 over size 14px 5 size 14px j with size 14px rightwards arrow on top end cell size 14px equals cell fraction numerator size 14px 6 size 14px i with size 14px rightwards arrow on top size 14px plus size 14px s size 14px j with size 14px rightwards arrow on top over denominator square root of size 14px 36 size 14px plus size 14px s to the power of size 14px 2 end root end fraction end cell row cell size 14px t size 14px i with size 14px rightwards arrow on top size 14px minus size 14px 4 over size 14px 5 size 14px j with size 14px rightwards arrow on top end cell size 14px equals cell fraction numerator size 14px 6 over denominator square root of size 14px 36 size 14px plus size 14px s to the power of size 14px 2 end root end fraction size 14px i with size 14px rightwards arrow on top size 14px plus fraction numerator size 14px s over denominator square root of size 14px 36 size 14px plus size 14px s to the power of size 14px 2 end root end fraction size 14px j with size 14px rightwards arrow on top end cell end table

Sehingga

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row t equals cell fraction numerator 6 over denominator square root of 36 plus s squared end root end fraction end cell row cell negative 4 over 5 end cell equals cell fraction numerator s over denominator square root of 36 plus s squared end root end fraction end cell end table end style

Karena begin mathsize 14px style e subscript a with rightwards arrow on top end subscript end style adalah vektor satuan, maka

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell open vertical bar e subscript a with rightwards arrow on top end subscript close vertical bar end cell equals 1 row cell square root of t squared plus open parentheses negative 4 over 5 close parentheses squared end root end cell equals 1 row cell t squared plus open parentheses negative 4 over 5 close parentheses squared end cell equals 1 row cell t squared plus 16 over 25 end cell equals 1 row cell t squared end cell equals cell 9 over 25 end cell row t equals cell plus-or-minus 3 over 5 end cell end table end style

Jika diperhatikan, begin mathsize 14px style fraction numerator 6 over denominator square root of 36 plus s squared end root end fraction end style  tidak mungkin bernilai negatif. Sehingga t tidak mungkin bernilai negatif, maka begin mathsize 14px style t equals 3 over 5 end style.

Sehingga

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row t equals cell fraction numerator 6 over denominator square root of 36 plus s squared end root end fraction end cell row cell 3 over 5 end cell equals cell fraction numerator 6 over denominator square root of 36 plus s squared end root end fraction end cell row cell square root of 36 plus s squared end root end cell equals 10 row cell 36 plus s squared end cell equals 100 row cell s squared end cell equals 64 row s equals cell plus-or-minus 8 end cell end table end style

Kemudian perhatikan bahwa

begin mathsize 14px style negative 4 over 5 equals fraction numerator s over denominator square root of 36 plus s squared end root end fraction end style

Ruas kiri bernilai negatif, sehingga ruas kanan juga harus bernilai negatif. Hal ini terpenuhi jika s negatif, maka s = -8.

Maka

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell s t end cell equals cell negative 8 times 3 over 5 end cell row blank equals cell negative 24 over 5 end cell end table end style  

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