Q 176: the ruses seem simple but the examples provided in books confuse me - when can and when can't you use cleave? (charging, full attack etc.)
Q 177: if you level up and take ranks in skill that is a class skill to one of your other classes (not the one you are levelling up at the moment), do you pay normal or double?
A 176: You can use cleave whenever you drop an opponent and you have another opponent within your threat range, period. (So if you're using a polearm and you drop an opponent, you can attack another opponent within 10 feet of you, but not one at 5 feet; if you then drop THAT one and have Great Cleave, you can attack yet another opponent within 10 feet).
A 177: You pay double. However, any skill that has been a class skill at some point has its cap maxed (so a Wizard 1/Fighter 19 can have 23 ranks in Spellcraft, for example, but he has to pay double for each rank as long as he's using Fighter skill points to buy them).