QUES: Exchanging "+" and "−" in the expression, i.e. permuting the two solutions of the equation can be viewed as a (very simple) group operation. Similar formulae are known for cubic and quartic equations, but do not exist in general for degree 5 and higher. Abstract properties of Galois groups associated with polynomials (in particular their solvability) give a criterion for polynomials that have all their solutions expressible by radicals, i.e. solutions expressible using solely addition, multiplication, and roots similar to the formula above.

Which group cannot be expressed using radicals?
What is the answer?
ANS: unanswerable
QUES: In 941, Igor led another major Rus' attack on Constantinople, probably over trading rights again. A navy of 10,000 vessels, including Pecheneg allies, landed on the Bithynian coast and devastated the Asiatic shore of the Bosphorus. The attack was well-timed, perhaps due to intelligence, as the Byzantine fleet was occupied with the Arabs in the Mediterranean, and the bulk of its army was stationed in the east. The Rus’ burned towns, churches, and monasteries, butchering the people and amassing booty. The emperor arranged for a small group of retired ships to be outfitted with Greek fire throwers and sent them out to meet the Rus’, luring them into surrounding the contingent before unleashing the Greek fire. Liutprand of Cremona wrote that "the Rus', seeing the flames, jumped overboard, preferring water to fire. Some sank, weighed down by the weight of their breastplates and helmets; others caught fire." Those captured were beheaded. The ploy dispelled the Rus’ fleet, but their attacks continued into the hinterland as far as Nicomedia, with many atrocities reported as victims were crucified and set up for use as targets. At last a Byzantine army arrived from the Balkans to drive the Rus' back, and a naval contingent reportedly destroyed much of the Rus' fleet on its return voyage (possibly an exaggeration since the Rus' soon mounted another attack). The outcome indicates increased military might by Byzantium since 911, suggesting a shift in the balance of power.

Why did the attack by the Rus go so well on the coast at the start?
What is the answer?
ANS: Byzantine fleet was occupied with the Arabs
QUES: The Houston area has over 150 active faults (estimated to be 300 active faults) with an aggregate length of up to 310 miles (500 km), including the Long Point–Eureka Heights fault system which runs through the center of the city. There have been no significant historically recorded earthquakes in Houston, but researchers do not discount the possibility of such quakes having occurred in the deeper past, nor occurring in the future. Land in some areas southeast of Houston is sinking because water has been pumped out of the ground for many years. It may be associated with slip along the faults; however, the slippage is slow and not considered an earthquake, where stationary faults must slip suddenly enough to create seismic waves. These faults also tend to move at a smooth rate in what is termed "fault creep", which further reduces the risk of an earthquake.

 Which of the geologic faults run through the center of Texas?
What is the answer?
ANS:
unanswerable