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Suppose a, b, c are three non-coplanar v...

Suppose a, b, c are three non-coplanar vectors, then
`((a+b+c)*((a+c) times(a+b)))/([a b c])="______"`

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To solve the given problem, we need to evaluate the expression: \[ \frac{(a+b+c) \cdot ((a+c) \times (a+b))}{[a \, b \, c]} \] where \( [a \, b \, c] \) represents the scalar triple product of the vectors \( a, b, c \). ### Step 1: Expand the Cross Product First, we need to compute the cross product \( (a+c) \times (a+b) \). Using the distributive property of the cross product, we have: \[ (a+c) \times (a+b) = a \times a + a \times b + c \times a + c \times b \] Since \( a \times a = 0 \) (the cross product of any vector with itself is zero), we can simplify this to: \[ (a+c) \times (a+b) = 0 + a \times b + c \times a + c \times b = a \times b + c \times a + c \times b \] ### Step 2: Substitute Back into the Expression Next, we substitute this result back into our original expression: \[ \frac{(a+b+c) \cdot (a \times b + c \times a + c \times b)}{[a \, b \, c]} \] ### Step 3: Distribute the Dot Product Now we will distribute the dot product: \[ (a+b+c) \cdot (a \times b + c \times a + c \times b) = (a+b+c) \cdot (a \times b) + (a+b+c) \cdot (c \times a) + (a+b+c) \cdot (c \times b) \] ### Step 4: Evaluate Each Dot Product 1. **First Term**: \( (a+b+c) \cdot (a \times b) \) The dot product of a vector with a cross product of two other vectors is zero if the vector is one of the two vectors being crossed. Thus, \( a \cdot (a \times b) = 0 \) and \( b \cdot (a \times b) = 0 \). Therefore: \[ (a+b+c) \cdot (a \times b) = c \cdot (a \times b) \] 2. **Second Term**: \( (a+b+c) \cdot (c \times a) \) Similarly, \( a \cdot (c \times a) = 0 \) and \( b \cdot (c \times a) = 0 \). Thus: \[ (a+b+c) \cdot (c \times a) = c \cdot (c \times a) = 0 \] 3. **Third Term**: \( (a+b+c) \cdot (c \times b) \) Again, \( a \cdot (c \times b) = 0 \) and \( b \cdot (c \times b) = 0 \). Therefore: \[ (a+b+c) \cdot (c \times b) = c \cdot (c \times b) = 0 \] ### Step 5: Combine Results Combining all these results, we find: \[ (a+b+c) \cdot (a \times b + c \times a + c \times b) = c \cdot (a \times b) + 0 + 0 = c \cdot (a \times b) \] ### Step 6: Final Expression Now, we can substitute this back into our original expression: \[ \frac{c \cdot (a \times b)}{[a \, b \, c]} \] ### Step 7: Recognize the Scalar Triple Product Recall that the scalar triple product \( [a \, b \, c] \) can also be expressed as \( a \cdot (b \times c) \). Therefore, we can conclude: \[ \frac{c \cdot (a \times b)}{[a \, b \, c]} = 1 \] Thus, the final answer is: \[ \boxed{1} \]
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