Astudent throws 3 coins in the air. find the probability that exactly 2 landed on heads, given that at least 2 landed on heads.

In problems of probability, it is best to find out the sample space or all the possible outcomes from throwing 3 coins in the air. 
S = {HHH, TTT, HHT}
 
The condition is at least 2 landed on heads (that means 2 or more). From the sample space, that can only be {THH, HHT, HTH, and HHH}.

Therefore, the probability is 3/4 since there are a total of 8 possible outcomes.

Do you need with the x value for the minimum? its always between the two intercepts for a parabola