Dua buah cermin datar X dan Y saling berhadapan dan membentuk sudut 60 derajat. Seberkas cahaya menuju X dengan sudut datang 60 derajat sehingga dipantulkan ke Y. Hitunglah sudut pantul dari cahaya yang meninggalkan Y

Explanation:

The text reads;

"The two flat mirrors X and Y face each other and form a 60-degree angle. One light goes to X with the angle coming 60 degrees until it is reflected Y. Calculate the angle of reflection of the light leaving Y".

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.