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Question

Find the coordinates of the vertices of a triangle, the equations of whose sides are
(i) x + y − 4 = 0, 2x − y + 3 = 0 and x − 3y + 2 = 0
(ii) y (t1 + t2) = 2x + 2a t1t2, y (t2 + t3) = 2x + 2a t2t3 and, y (t3 + t1) = 2x + 2a t1t3.

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Solution

(i) x + y − 4 = 0, 2x − y + 3 = 0 and x − 3y + 2 = 0

x + y − 4 = 0 ... (1)

2x − y + 3 = 0 ... (2)

x − 3y + 2 = 0 ... (3)

Solving (1) and (2) using cross-multiplication method:

x3-4=y-8-3=1-1-2x=13, y=113

Solving (1) and (3) using cross-multiplication method:

x2-12=y-4-2=1-3-1x=52, y=32

Similarly, solving (2) and (3) using cross-multiplication method:

x-2+9=y3-4=1-6+1x=-75, y=15

Hence, the coordinates of the vertices of the triangle are 13, 113, 52, 32 and -75, 15.

(ii) y (t1 + t2) = 2x + 2a t1t2, y (t2 + t3) = 2x + 2a t2t3 and y (t3 + t1) = 2x + 2a t1t3

2x − y (t1 + t2) + 2a t1t2 = 0 ... (1)

2x − y (t2 + t3) + 2a t2t3 = 0 ... (2)

2x − y (t3 + t1) + 2a t1t3 = 0 ... (3)

Solving (1) and (2) using cross-multiplication method:

x-2at2t3t1+t2+2at1t2t2+t3=y4at1t2-4at2t3=1-2t2+t3+2t1+t2x2at22t1-t3=y4at2t1-t3=12t1-t3x=at22, y=2at2

Solving (1) and (3) using cross-multiplication method:

x-2at1t3t1+t2+2at1t2t3+t1=y4at1t2-4at1t3=1-2t3+t1+2t1+t2x2at12t2-t3=y4at1t2-t3=12t2-t3x=at12, y=2at1

Similarly, solving (2) and (3) using cross-multiplication method:

x-2at1t3t2+t3+2at2t3t3+t1=y4at2t3-4at1t3=1-2t3+t1+2t2+t3x2at32t2-t1=y4at3t2-t1=12t2-t1x=at32, y=2at3

Hence, the coordinates of the vertices of the triangle are at12, 2at1, at22, 2at2 and at32, 2at3.

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