810 A high school mathematics contest
2.Solve the equation
x^2 −|x|−1=0.3.Let(an)be an arithmetic sequence. Ifap = qandaq = p, find
ap+q.4.A five-digit number is called a mountain number if the first three
digits are increasing and the last three are decreasing. For exam-
ple, 34541 is a mountain number, but 34534 is not. How many
mountain numbers are greater than 70000?