A triangle has corners at (2, 1 )(2,1), ( 1, 3 )(1,3), and (5 , 5 )(5,5). If the triangle is dilated by 3 x3x around (1, 6)(1,6), what will the new coordinates of its corners be?

2 Answers
May 10, 2017

(2,1)to(4,-9)(2,1)(4,9)
(1,3)to(1,-3)(1,3)(1,3)
(5,5)to(13,3)(5,5)(13,3)

Explanation:

The vector equation of a line from (1, 6)(1,6) to (2,1)(2,1) is:

(x,y)=(1,6)+t((2-1)hati+(1-6)hatj)(x,y)=(1,6)+t((21)ˆi+(16)ˆj)

Perform the subtraction within the vector:

(x,y)=(1,6)+t(hati-5hatj)" [1]"(x,y)=(1,6)+t(ˆi5ˆj) [1]

The vector equation of a line from (1, 6)(1,6) to (1,3)(1,3) is:

(x,y)=(1,6)+t((1-1)hati+(3-6)hatj)(x,y)=(1,6)+t((11)ˆi+(36)ˆj)

Perform the subtraction within the vector:

(x,y)=(1,6)+t(-3hatj)" [2]"(x,y)=(1,6)+t(3ˆj) [2]

The vector equation of a line from (1, 6)(1,6) to (5,5)(5,5) is:

(x,y)=(1,6)+t((5-1)hati+(5-6)hatj)(x,y)=(1,6)+t((51)ˆi+(56)ˆj)

Perform the subtraction within the vector:

(x,y)=(1,6)+t(4hati-hatj)" [3]"(x,y)=(1,6)+t(4ˆiˆj) [3]

Here are the 3 vector equations:

(x,y)=(1,6)+t(hati-5hatj)" [1]"(x,y)=(1,6)+t(ˆi5ˆj) [1]
(x,y)=(1,6)+t(-3hatj)" [2]"(x,y)=(1,6)+t(3ˆj) [2]
(x,y)=(1,6)+t(4hati-hatj)" [3]"(x,y)=(1,6)+t(4ˆiˆj) [3]

To obtain the new points, evaluate equations [1], [2], and [3] at t = 3

(x,y)=(1,6)+3(hati-5hatj)(x,y)=(1,6)+3(ˆi5ˆj)
(x,y)=(1,6)+3(-3hatj)(x,y)=(1,6)+3(3ˆj)
(x,y)=(1,6)+3(4hati-hatj)(x,y)=(1,6)+3(4ˆiˆj)

(x,y)=(4,-9)(x,y)=(4,9)
(x,y)=(1,-3)(x,y)=(1,3)
(x,y)=(13,3)(x,y)=(13,3)

May 10, 2017

(4,-9),(1,-3),(13,3)(4,9),(1,3),(13,3)

Explanation:

"let " A=(2,1),B=(1,3),C=(5,5)" and " D=(1,6)let A=(2,1),B=(1,3),C=(5,5) and D=(1,6)

"and " A',B',C'" be the images of A,B" and "C
"under the dilatation"

vec(DA)=ula-uld=((2),(1))-((1),(6))=((1),(-5))

rArrvec(DA')=3((1),(-5))=((3),(-15))

rArrA'=(1+3,6-15)=(4,-9)
color(blue)"--------------------------------------------------"

vec(DB)=ulb-uld=((1),(3))-((1),(6))=((0),(-3))

rArrvec(DB')=3((0),(-3))=((0),(-9))

rArrB'=(1+0,6-9)=(1,-3)
color(blue)"--------------------------------------------------"

vec(DC)=ulc-uld=((5),(5))-((1),(6))=((4),(-1))

rArrvec(DC')=3((4),(-1))=((12),(-3))

rArrC'=(1+12,6-3)=(13,3)
color(blue)"-------------------------------------------------"