What is the conditional probability that exactly four heads appear when a fair coin is flipped five times given that the first flip came up tail?

Presumably, the coin tosses are independent of one another, so

But if the coin flips are not independent, then we can't really say anything about this probability without any more information about how the flips are related...

answer: the angel abc is 30°,and the abc is a triangle where the angel bac is 90°

so ac is the half of 24=12ft,and from the pythagorean theorem we find ba

ba=√bc^2-ac^2=√576-144=√432=12√3ft

so bac is 12+12√3=12(1+√3)ft