Finding coordinates of points using vectors? (See picture)

enter image source here

1 Answer
Nov 16, 2017

See below.

Explanation:

enter image source here

To find the coordinates of A B C, we need to find the intersection of the vector lines. This can be done equating each pair of vector lines.

To find point A we will use vector lines AB and AC. See diagram.

#AB =AC#

#((0),(2))+r((2),(1))=((0),(5))+t((1),(-1))#

#color(white)(->)2r=t#
#2+r=5-t#

Solving for #r# and #t#:

#r=3-t#

#2(3-t)=t=>t=2#

#2r=2=>r=1#

Using these in #AB =AC#

#((0),(2))+1((2),(1))=((0),(5))+2((1),(-1))#

#((2),(3))=((2),(3))#

Coordinate of A: #color(white)(8)( 2 color(white)(1), 3 )#

To find point B we will use vector lines AB and BC.

#AB = BC#

#((0),(2))+r((2),(1))=((8),(6))+s((-1),(-2))#

#color(white)(888)2r=8-s#
#2+r=6-2s#

#r=4-2s#

#2(4-2s)=8-s=>s=0#
#2+r=6-2(0)=>r=4#

Using these in #AB =BC#

#((0),(2))+4((2),(1))=((8),(6))+0((-1),(-2))#

#((8),(6))=((8),(6))#

Coordinate of B: #color(white)(8)( 8 color(white)(1), 6 )#

To find point C we will use vector lines AC and BC.

#AC=BC#

#((0),(5))+t((1),(-1))=((8),(6))+s((-1),(-2))#

#color(white)(8888)t=8-s#
#5-t=6-2s#

#5-(8-s)=6-2s=>s=3#
#t=8-3=>t=5#

Using these in #AC =BC#

#((0),(5))+5((1),(-1))=((8),(6))+3((-1),(-2))#

#((5),(0))=((5),(0))#

Coordinate of C: #color(white)(8)( 5 color(white)(1), 0 )#

To calculate the lengths of the sides, we could either use the distance formula or find vectors #vec(AB), vec(AC) and vec(CB)# and find their magnitude.

Using vectors.

#vec(AB)=((8),(6))-((2),(3))=((6),(3))#

#vec(AC)=((5),(0))-((2),(3))=((3),(-3))#

#vec(CB)=((8),(6))-((5),(0))=((3),(6))#

#||AB||=sqrt((6^2)+(3^2))=sqrt(45)=3sqrt(5)#

#||AC||=sqrt((3^2)+(-3^2))=sqrt(18)=3sqrt(2)#

#||CB||=sqrt((3^2)+(6^2))=sqrt(45)=3sqrt(5)#

Sides AB and BC are of equal length.

Coordinates:

#A=(2 , 3)#
#B=( 8 , 6 )#
#C=( 5 ,0 )#

Side lengths:

#AB=3sqrt(5)#
#BC=3sqrt(5)#
#AC=3sqrt(2)#