Answer: The expression which must fill in each blank space to complete step 3 is; Choice B; Cos(A)Cos(B).
Which expression must fill in each blank space?
From the task content; It follows that the mathematical evaluation is in a bid to derive the Trigonometric identity for Tan (A-B).
From observation, it follows that the required expression is; cos(A)sin(B). This is because upon division of each term by the expression, the result is as in Step 4.