Why do authors make certain words bold, italicized, or underlined?

Answer above be like:

answer: this problem has only trivial solutions, with all points on the same line. x=5 or x=7/5.

step-by-step explanation:

there are three triangles, and three unknowns: x, y=length of middle segment, and z=cos(angles marked with red arc).

we need

and law of cosines,

the three equations are

see attached image for solution.

whose power in the senate is equal to the power of the speaker of the house?