Question

Review the proof of cos(A - B) = cosAcosB + sinAsinB.

Answer 1

Answer:

the answer is 2 and 1 or B

Step-by-step explanation:

Answer 2

Answer:

Option (2)

Step-by-step explanation:

Step 1.

$\sqrt{(\text{cosA-cosB})^2+(\text{sinA-sinB})^2}=\sqrt{(cos(A-B)-1)^2+(sin(A-B)-0)^2}$

Step 2.

(cosA - cosB)² + (sinA - sinB)² = [cos(A - B) - 1]² + [sin(A - B) - 0]²

Step 3.

cos²A + cos²B - 2cosAcosB + sin²A + sin²B - 2sinAsinB  = cos²(A - B) + 1 - 2cos(A - B) + sin²(A - B)

Step 4.

2 - 2cosAcosB - 2sinAsinB = 1 - 2cos(A - B) + 1

Step 5.

cosAcosB + sinAsinB = cos(A - B)

Therefore, Option (2) will be the answer.