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Let $$ABC$$ be a triangle such that $$\vec{BC} = \vec{a}$$, $$\vec{CA} = \vec{b}$$, $$\vec{AB} = \vec{c}$$, $$|\vec{a}| = 6\sqrt{2}$$, $$|\vec{b}| = 2\sqrt{3}$$ and $$\vec{b} \cdot \vec{c} = 12$$. Consider the statements:
$$S_1: |\vec{a} \times (\vec{b} + \vec{c})| \times |\vec{b} - \vec{c}| = 6(2\sqrt{2} - 1)$$
$$S_2: \angle ABC = \cos^{-1}\sqrt{\dfrac{2}{3}}$$
Then
Given,
$$\vec{BC}=\vec a,\qquad \vec{CA}=\vec b,\qquad \vec{AB}=\vec c$$
Also,
$$|\vec a|=6\sqrt2,\qquad |\vec b|=2\sqrt3,\qquad \vec b\cdot\vec c=12$$
Since
$$\vec a+\vec b+\vec c=0,$$
we get
$$\vec c=-(\vec a+\vec b)$$
Now,
$$\vec b\cdot\vec c=12$$
$$\vec b\cdot(-\vec a-\vec b)=12$$
$$-\vec a\cdot\vec b-|\vec b|^2=12$$
$$-\vec a\cdot\vec b-(2\sqrt3)^2=12$$
$$-\vec a\cdot\vec b-12=12$$
$$\vec a\cdot\vec b=-24$$
Now find
$$|\vec c|^2$$
$$|\vec c|^2=|\vec a+\vec b|^2$$
$$=|\vec a|^2+|\vec b|^2+2\vec a\cdot\vec b$$
$$=(6\sqrt2)^2+(2\sqrt3)^2+2(-24)$$
$$=72+12-48$$
$$=36$$
Hence,
$$|\vec c|=6$$
Now check statement $$S_1.$$
Since
$$\vec b+\vec c=-\vec a,$$
$$\vec a\times(\vec b+\vec c)=\vec a\times(-\vec a)=0$$
Therefore,
$$|\vec a\times(\vec b+\vec c)|=0$$
Hence,
$$|\vec a\times(\vec b+\vec c)|\times|\vec b-\vec c|=0$$
which is not equal to
$$6(2\sqrt2-1)$$
Therefore,
$$S_1$$ is false.
Now check $$S_2.$$
Angle $$ABC$$ is the angle between
$$\vec{BA}=-\vec c$$
and
$$\vec{BC}=\vec a$$
Hence,
$$\cos\angle ABC=\frac{(-\vec c)\cdot\vec a}{|\vec c||\vec a|}$$
Now,
$$\vec c=-(\vec a+\vec b)$$
$$\vec a\cdot\vec c=\vec a\cdot(-\vec a-\vec b)$$
$$=-|\vec a|^2-\vec a\cdot\vec b$$
$$=-72-(-24)$$
$$=-48$$
Thus,
$$(-\vec c)\cdot\vec a=48$$
Therefore,
$$\cos\angle ABC=\frac{48}{6\cdot6\sqrt2}$$
$$=\frac{48}{36\sqrt2}$$
$$=\frac4{3\sqrt2}$$
$$=\frac{2\sqrt2}{3}$$
$$=\sqrt{\frac89}$$
which is not equal to
$$\sqrt{\frac23}$$
Hence,
$$S_2$$ is false.
Therefore,
$$\boxed{\text{Both }S_1\text{ and }S_2\text{ are false}}$$.
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