Answer:
Step-by-step explanation:
This is a fascinating question. It turns out to be true because of the relationship between a 30 degree angle and a 60 degree angle
The answer is that the product of sin30*sin60 = cos(30)*cos(60). This happens because sin(60) = cos(90-60) = cos(30)
Other angles will do the same thing sin36 * sin54 = cos(54)*cos(36)