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Problem If a ⋅ b \mathbf{a} \cdot \mathbf{b} a ⋅ b and c \mathbf{c} c are any three non-zero vectors, then the component of a × ( b × c ) \mathbf{a} \times (\mathbf{b} \times \mathbf{c}) a × ( b × c ) perpendicular to b \mathbf{b} b is
a. a × ( b × c ) + ( a × b ) ⋅ ( c × a ) ∣ b ∣ 2 b \mathbf{a} \times (\mathbf{b} \times \mathbf{c}) + \frac{(\mathbf{a} \times \mathbf{b}) \cdot (\mathbf{c} \times \mathbf{a})}{|\mathbf{b}|^2} \mathbf{b} a × ( b × c ) + ∣ b ∣ 2 ( a × b ) ⋅ ( c × a ) b
b. a × ( b × c ) + ( a × c ) ⋅ ( a × b ) ∣ b ∣ 2 b \mathbf{a} \times (\mathbf{b} \times \mathbf{c}) + \frac{(\mathbf{a} \times \mathbf{c}) \cdot (\mathbf{a} \times \mathbf{b})}{|\mathbf{b}|^2} \mathbf{b} a × ( b × c ) + ∣ b ∣ 2 ( a × c ) ⋅ ( a × b ) b
c. a × ( b × c ) + ( b × c ) ⋅ ( b × a ) ∣ b ∣ 2 b \mathbf{a} \times (\mathbf{b} \times \mathbf{c}) + \frac{(\mathbf{b} \times \mathbf{c}) \cdot (\mathbf{b} \times \mathbf{a})}{|\mathbf{b}|^2} \mathbf{b} a × ( b × c ) + ∣ b ∣ 2 ( b × c ) ⋅ ( b × a ) b
d. a × ( b × c ) + ( a × b ) ⋅ ( b × c ) ∣ b ∣ 2 b \mathbf{a} \times (\mathbf{b} \times \mathbf{c}) + \frac{(\mathbf{a} \times \mathbf{b}) \cdot (\mathbf{b} \times \mathbf{c})}{|\mathbf{b}|^2} \mathbf{b} a × ( b × c ) + ∣ b ∣ 2 ( a × b ) ⋅ ( b × c ) b
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