Option c: 
Step-by-step explanation:
The expression is 
Applying the exponent rule, we have,

Multiplying the denominator,

Rewriting this expression,

Cancelling the common terms, we have,

Thus, the expression equivalent to
is 
Answer:
b = 6 or b = -6 (non-zero vectors)
b = 0 (zero vector)
Step-by-step explanation:
Two vectors
and
are orthogonal if their dot product is equal to 0, or in other words

In your case,

Hence, if vectors a and b are orthogonal, then

Note, then if b = 0, then
and zero-vector is orthogonal to any other vectors.
Thus, b = 6 or b = -6.
Answer:
Step-by-step explanation: