Two lines are parallel if and only if their slopes are equal and they are not coincident or if they both are vertical and therefore have undefined slopes.

Two lines are perpendicular if the product of their slopes is − 1 or one has a slope of 0 ( a horizontal line ) and the other has an undefined slope ( a vertical line ).

By the end of World War Two, the US had built eight new wind tunnels, including the largest one in the world at Moffett Field near Sunnyvale, California, which was designed to test full size aircraft at speeds of less than 250 mph and a vertical wind tunnel at Wright Field, Ohio, where the wind stream is upwards for the testing of models in spin situations and the concepts and engineering designs for the first primitive helicopters flown in the US.

Two vertical cladograms, the ancestor at the bottom

Two intersections are said to be adjacent if they are connected by a horizontal or vertical line with no other intersections between them.

Two intersections are said to be adjacent if they are distinct and connected by a horizontal or vertical line with no other intersections between them.

Two new power-ups were added: a golden item containing a new weapon power-up which gives the player green, vertical lasers that do pierce through enemies, and a rainbow-colored item that powers up all the players weapons.

Two vertical iron bars with an iron cross-piece allow pots to be hung at various heights or over different temperatures of fire.

Two of its elements ( the upper triangle and the right vertical bar ) form the angular base frame for the other characters.

Two of the more recently constructed bridges ( at Broadway and Park Avenue ) are vertical lift replacements of swing spans, where the previous bridges had become obsolete for the subway and railroad that used them.

Two different types of harbor cranes can be identified with a varying geographical distribution: While gantry cranes which pivoted on a central vertical axle were commonly found at the Flemish and Dutch coastside, German sea and inland harbors typically featured tower cranes where the windlass and treadwheels were situated in a solid tower with only jib arm and roof rotating.

Two smaller paintings are attached to the top and bottom of the central picture, and two vertical pictures on either side, filled with sphinxes, Pan, and two satyrs.

Two different diachronic mechanisms may give rise to a vertical vowel system.

Two versions of the Montenegrin flag are in use, horizontal, mostly used outdoor ; and vertical, mostly used indoor.

Two large avenues were discovered, with an amplitude of 7 meters, along with vertical and horizontal streets that divided the urban area into city blocks.

Two vertical sight apertures are arranged opposite each other and can be rotated along the graduated arc of the horizontal table.

Two main shapes of Welsh hat were made during the 19th century: those with drum shaped ( vertical sided ) crowns were worn in north-west Wales, and those with slightly tapering crowns were found in the rest of Wales.

Two prominent black vertical bars appear just posterior of the gills.

The Flag of Orocovis is formed by five vertical stripes: Two green stripes at the ends, representing the territories of Aibonito and Barranquitas ; and a blue one in the center representing the regional domain of the cacique Orocobix prior to the Spanish colonization.

Two vertical-axis-aligned cylinders intersect when, simultaneously, their projections on the vertical axis intersect – which are two line segments – as well their projections on the horizontal plane – two circular disks.

File: Züricher Spielzeugmuseum 1000717. jpg | Two 1920 Bing steamrollers and an 1885 Schönner vertical model steam engine

Two examples of dome-top trunks: one is a vertical slat trunk, the other is a barrel-stave trunk

Two " windows " in a vertical shaft at depths of 220 – 250 m were documented on the cave map but remained unexplored.

Two balls are dedicated to a specific hand with vertical throws, and the third ball is thrown horizontally between the two hands.

The legend recorded by Manetho was that Menes, the first pharaoh to unite the Two Lands, established his capital on the banks of the Nile by diverting the river with dikes.

Two Jurassic kimberlite dikes exist in Pennsylvania.

Two dikes built by Man dictate it plan today.

Two smaller dams, called dikes, were built during the 1961 expansion to increase the lake's capacity.

Two days later, some 30 of them had struck at a convoy off Bougie, sinking a troopship -- and it had been that very night that the Me-210 had made its first appearance.

Two millions were added to what had been set aside for it in Mrs. Meeker's lifetime, and the proviso made that as long as Brian Thayer continued to discharge his duties as administrator of the fund to the satisfaction of the board of trustees ( hereinafter appointed by the bank administering the estate ) he was to be retained in his present capacity at a salary commensurate with the increased responsibilities enlargement of the fund would entail.

Two late Sonatas, Op. 110 and 111, were played with similar insight, the disarming simplicities of the Op. 111 Adagio made plain without ever becoming obvious.

Two binary abaci constructed by Dr. Robert C. Good, Jr., made from two Chinese abaci

Two, from the Venus tablet of Ammisaduqa ( compiled in Babylon around 1700 BCE ) are reported to have been made during the reign of king Sargon of Akkad ( 2334 – 2279 BCE ).

Grant then made a few more albums before dropping out of college to pursue a career in music — Never Alone, followed by a pair of live albums in 1981 ( In Concert and In Concert Volume Two ), both backed by an augmented edition of the DeGarmo & Key band.

Two conciliar letters were prepared, one to the clergy and faithful of Alexandria, the other to the bishops of Egypt and Libya, in which the will of the Council was made known.

The characters have made cameo appearances ( either visually or only voices ) and have been referenced in numerous television shows, such as Friends, Two and a Half Men, Celebrity Deathmatch, Robot Chicken, Space Ghost Coast to Coast, and Saturday Night Live ( TV Funhouse ), in films such as Airheads, Clueless, Austin Powers: International Man of Mystery and Jackass 3D, and even parodied in children shows such as Tiny Toon Adventures, Regular Show and Arthur.

Two years later, WHDH-FM was licensed, and on November 26, 1957, WHDH-TV made its début as an ABC affiliate on channel 5.

In 860, an attack was made on the city by a new principality set up a few years earlier at Kiev by Askold and Dir, two Varangian chiefs: Two hundred small vessels passed through the Bosporus and plundered the monasteries and other properties on the suburban Prince's Islands.

Two women made a pact to eat their children ; after the first mother cooked her child the second mother ate it but refused to reciprocate by cooking her own child.

Two other satellites made observations at the time of the impact: the Ulysses spacecraft, primarily designed for solar observations, was pointed towards Jupiter from its location 2. 6 AU away, and the distant Voyager 2 probe, some 44 AU from Jupiter and on its way out of the Solar System following its encounter with Neptune in 1989, was programmed to look for radio emission in the 1 – 390 kHz range.

He received accolades for his portrayal of Sydney Carton in a made for television version of A Tale of Two Cities ( 1980 ), co-starred with Dennis Hopper in The Osterman Weekend ( 1983 ), which was based on the Robert Ludlum novel of the same name, and co-starred with Goldie Hawn in Protocol ( 1984 ).

Two English translations of the Various History, by Fleming ( 1576 ) and Stanley ( 1665 ) made Aelian's miscellany available to English readers, but after 1665 no English translation appeared, until three English translations appeared almost simultaneously: James G. DeVoto, Claudius Aelianus: Ποιϰίλης Ἱοτορίας (" Varia Historia ") Chicago, 1995 ; Diane Ostrom Johnson, An English Translation of Claudius Aelianus ' " Varia Historia ", 1997 ; and N. G. Wilson, Aelian: Historical Miscellany in the Loeb Classical Library.

Two FRUD members were made cabinet members, and in the presidential elections of 1999 the FRUD campaigned in support of the RPP.

Two FRUD members were made cabinet members, and in the presidential elections of 1999 the FRUD campaigned in support of the RPP.

Two were libel suits, one against Day and her publishers over comments she made about Rosenthal in her book in which he sought damages.

Two developments made a difference in the 1960s.

Two days later, the same three guilds made a second attempt and after almost 4 hours, successfully killed the sleeper.

Two Cities Films, an independent production company also made some important films including This Happy Breed ( 1944 ), Blithe Spirit ( 1945 ) and Sir Laurence Olivier's Henry V ( 1944 ) and Hamlet ( 1948 ).

Two years later he was in London, where he was made a fellow of the Royal Society.

Two cuts are made around the vagina, then sutures are put in place to tighten it to the size of a pinhole.

Two important payments are made to a franchisor: ( a ) a royalty for the trademark and ( b ) reimbursement for the training and advisory services given to the franchisee.

Formula 3000 replaced Formula Two, and was so named because the engines used initially were 3. 0 L ( 183ci ) Cosworth DFV engines made obsolete by popularization of 1. 5 L turbocharged engines in Formula One.

Two Guinean MiGs made a low flyover of Freetown and Toure placed the Guinean military on alert ' because of the serious troubles affecting the fraternal peoples of Sierra Leone.