Answer on Question #81393 – Math – Linear Algebra
Question
Check whether the vector ( 2 3 , 2 ) (2\sqrt{3}, 2) ( 2 3 , 2 ) is equally inclined to the vectors ( 2 , 2 3 ) (2, 2\sqrt{3}) ( 2 , 2 3 ) and ( 4 , 0 ) (4, 0) ( 4 , 0 ) .
Solution
Let a ⃗ = ( 2 3 , 2 ) , b ⃗ = ( 2 , 2 3 ) \vec{a} = (2\sqrt{3}, 2), \vec{b} = (2, 2\sqrt{3}) a = ( 2 3 , 2 ) , b = ( 2 , 2 3 ) and c ⃗ = ( 4 , 0 ) \vec{c} = (4, 0) c = ( 4 , 0 ) .
Find dot product
a ⃗ ⋅ b ⃗ = 2 3 ( 2 ) + 2 ( 2 3 ) = 8 3 \vec{a} \cdot \vec{b} = 2\sqrt{3}(2) + 2(2\sqrt{3}) = 8\sqrt{3} a ⋅ b = 2 3 ( 2 ) + 2 ( 2 3 ) = 8 3 a ⃗ ⋅ c ⃗ = 2 3 ( 4 ) + 2 ( 0 ) = 8 3 \vec{a} \cdot \vec{c} = 2\sqrt{3}(4) + 2(0) = 8\sqrt{3} a ⋅ c = 2 3 ( 4 ) + 2 ( 0 ) = 8 3 ∣ a ⃗ ∣ = ( 2 3 ) 2 + ( 2 ) 2 = 4 |\vec{a}| = \sqrt{(2\sqrt{3})^2 + (2)^2} = 4 ∣ a ∣ = ( 2 3 ) 2 + ( 2 ) 2 = 4 ∣ b ⃗ ∣ = ( 2 ) 2 + ( 2 3 ) 2 = 4 |\vec{b}| = \sqrt{(2)^2 + (2\sqrt{3})^2} = 4 ∣ b ∣ = ( 2 ) 2 + ( 2 3 ) 2 = 4 ∣ c ⃗ ∣ = ( 4 ) 2 + ( 0 ) 2 = 4 |\vec{c}| = \sqrt{(4)^2 + (0)^2} = 4 ∣ c ∣ = ( 4 ) 2 + ( 0 ) 2 = 4 cos β = a ⃗ ⋅ b ⃗ ∣ a ⃗ ∣ ∣ b ⃗ ∣ = 8 3 4 ⋅ 4 = 3 2 \cos \beta = \frac{\vec{a} \cdot \vec{b}}{|\vec{a}||\vec{b}|} = \frac{8\sqrt{3}}{4 \cdot 4} = \frac{\sqrt{3}}{2} cos β = ∣ a ∣∣ b ∣ a ⋅ b = 4 ⋅ 4 8 3 = 2 3 cos γ = a ⃗ ⋅ c ⃗ ∣ a ⃗ ∣ ∣ c ⃗ ∣ = 8 3 4 ⋅ 4 = 3 2 \cos \gamma = \frac{\vec{a} \cdot \vec{c}}{|\vec{a}||\vec{c}|} = \frac{8\sqrt{3}}{4 \cdot 4} = \frac{\sqrt{3}}{2} cos γ = ∣ a ∣∣ c ∣ a ⋅ c = 4 ⋅ 4 8 3 = 2 3
Therefore, the vector ( 2 3 , 2 ) (2\sqrt{3}, 2) ( 2 3 , 2 ) is equally inclined to the vectors ( 2 , 2 3 ) (2, 2\sqrt{3}) ( 2 , 2 3 ) and ( 4 , 0 ) (4, 0) ( 4 , 0 ) .
Answer: the vector ( 2 3 , 2 ) (2\sqrt{3}, 2) ( 2 3 , 2 ) is equally inclined to the vectors ( 2 , 2 3 ) (2, 2\sqrt{3}) ( 2 , 2 3 ) and ( 4 , 0 ) (4, 0) ( 4 , 0 ) .
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