Answer: 0.55
Explanation:
According to the trigonometry, in a right triangle :

Given : A 50-foot tree casts a shadow 75 feet long.
Here , Side opposite to
= 50 feet
In right triangle formed by tree , Let the hypotenuse be h.
According to the Pythagoras theorem, we have

Then,

Hence, the sine of the angle between the ground and the line that connects the tip of the shadow to the top of the tree is approximately 0.55.