Which option below best describes the difference between an experiment and an observational study? a. the values in an experiment are chosen at random, but not in an observational study. b. the values in an observational study are chosen at random, but not in an experiment. c. the groups in an experiment are chosen at random, but not in an observational study. d. the groups in an observational are chosen at random, but not in an experiment.

Proceed as in example 3 in section 6.1 to rewrite the given expression using a single power series whose general term involves xk. ∞ n(n − 1)cnxn − 2 n = 2 − 4 ∞ ncnxn n = 1 + ∞ cnxn n = 0

Luke started a weight-loss program. the first week, he lost x pounds. the second week, he lost pounds less than times the pounds he lost the first week. the third week, he lost 1 pound more than of the pounds he lost the first week. liam started a weight-loss program when luke did. the first week, he lost 1 pound less than times the pounds luke lost the first week. the second week, he lost 4 pounds less than times the pounds luke lost the first week. the third week, he lost pound more than times the pounds luke lost the first week.

Write the factored form of this trinomial 9x^2+18x-7