The expression $-1 = ijk$ is often encountered in the context of quaternions, which is a number system that extends complex numbers. The symbols $i$, $j$, and $k$ are the fundamental units of quaternions and satisfy specific multiplication rules.

In quaternion algebra:

• $i^2 = j^2 = k^2 = ijk = -1$
• $ij = k$
• $jk = i$
• $ki = j$
• And, their products are non-commutative: $ij \neq ji$, etc.

So, the expression $ijk = -1$ is correct within the rules of quaternion algebra. It represents the result of multiplying the three imaginary units of quaternions, which is equal to $-1$.

Would you like further clarification on quaternions or their properties? Let me know if you want more details.

Here are 5 related questions:

1. What is the structure of quaternions, and how are they used in 3D rotations?
2. How does quaternion multiplication differ from regular complex numbers?
3. Can you explain how the non-commutative property of quaternions works?
4. What are the applications of quaternions in computer graphics and physics?
5. How do quaternions relate to Euler angles and rotation matrices?

Tip: Quaternions are particularly useful for interpolating rotations in 3D space, making them a staple in computer graphics and robotics.