Three consonants carry one idea: wide. From it Hebrew measures width, names the broad open street you walk down, the vast space you breathe in, and the act of expanding something. The same root gives the everyday word for a street, רְחוֹב, because a street is simply "the wide place" between the houses. Every word here is verified against pealim, niqqud included.
The same root runs through the verb system. Each binyan is a voice: it bends the one idea into active, passive, causative or reciprocal. Tap to hear.
The contrast is the whole lesson: the pa'al לִרְחֹב is a state, "to be wide", while the causative hif'il לְהַרְחִיב acts on an object, "to make it wide". Its action-noun הַרְחָבָה (expansion) appears in the groups below.
Same root letters, different noun moulds (mishkalim). The mould tells you the function: who does it, the act of doing it, or the thing produced.
Strip the prefixes, suffixes and vowels. Three consonants remain, and the meaning lives there.