thisisclearlynotwhatwewereexpectingforananswerhereandsoweneedtodeterminejustwhatisgoingon.Weâllleaveittoyoutoverifythis
butifyoufindtheslopeandy-interceptsforthesetwolinesyouwillfindthatbothlineshaveexactlythesameslopeandbothlineshaveexactlythesamey-intercept.So
whatdoesthismeanforus?Welliftwolineshavethesameslopeandthesamey-interceptthenthegraphsofthetwolinesarethesamegraph.Inotherwords
thegraphsofthesetwolinesarethesamegraph.Inthesecasesanysetofpointsthatsatisfiesoneoftheequationswillalsosatisfytheotherequation.Also
recallthatthegraphofanequationisnothingmorethanthesetofallpointsthatsatisfiestheequation.Inotherwords
thereisaninfinitesetofpointsthatwillsatisfythissetofequations.Inthesecaseswedowanttowritedownsomethingforasolution.So
whatweâlldoissolveoneoftheequationsforoneofthevariables(itdoesnâtmatterwhichyouchoose).Weâllsolvethefirstfory.2x+5y=15y=2x1y=25×15©PaulDawkinsAlgebraâ365â