What is the relationship between a reflected wave's "angle of incidence" and "angle of reflection"?

those 2 angles add up to 180 degrees

those 2 angles are always equal

those 2 angle add up to 90 degrees

the "angle of reflection" minus the "angle of incidence" equal 45 degrees

According to the law of reflection, the angle of incidence is always equal to the angle of reflection.

Answer Statement: B

Explanation:

Suppose there is a light ray that falls on a plane surface or mirror and gets reflected. If we draw a normal going through the point where both the rays (incident and reflected rays) meet, we can easily observe that they both make an angle with this normal N say i and r, respectively.

With specific observation it's concluded as the statement and hence, the law; that the angle of incidence i and the angle of reflection r are equal with respect to the normal drawn at the point the point they both meet when the all of them are correspondent to the same surface.

Hence,

Angle of Incidence = Angle of reflection

Now, coming to the point that what are the other angles thus formed along with the surface, can be calculated by simply subtracting the angle of incidence and the angle of reflection from 90 degree, being the normal on the plane surface or the mirror.

Both the angle doesn't necessarily made a 180 degree angle. In fact, it's quite difficult to think about such an angle. Neither both the angles are of 90 degree. Hence, their difference may also vary.

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form