A Triangle with Vertices at (X1, Y1), (X2, Y2), and (X3

question 367

Multiple Choice

A triangle with vertices at (x1, y1) , (x2, y2) , and (x3, y3) has area equal to the absolute value of D, where $$D = \frac { 1 } { 2 } \left| \begin{array} { l l l } x _ { 1 } & y _ { 1 } & 1 \\x _ { 2 } & y _ { 2 } & 1 \\x _ { 3 } & y _ { 3 } & 1\end{array} \right|$$ Find the area of the triangle having vertices at P, Q, and R.
- $P ( 1,5 ) , Q ( 5,7 ) , R ( 8,1 )$

• A) 12
• B) 30
• C) 15
• D) 0

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