Let the vertices Q and R of the triangle PQR lie on the line x+35 = y-12 = z+43, QR = 5 and the coordinates of the point P be (0, 2, 3). If the area of the triangle PQR is mn then :
- 2m - 5 21 n = 0
- m - 5 21 n = 0
- 5m - 21 2 n = 0
- 5m - 2 21 n = 0
Answer
(1) 2m - 5 21 n = 0
Solution
The line passes through A(-3, 1, -4) with direction b = 5 i + 2 j + 3 k.
AP = 3 i + j + 7 k
AP b = vmatrix i & j & k \ 3 & 1 & 7 \ 5 & 2 & 3 vmatrix = -11 i + 26 j + k
Distance of P from the line (height of the triangle):
h = | AP b|| b| = 121 + 676 + 1 38 = 79838 = 21
Area of PQR = 12 QR h = 12 5 21 = 5 212
mn = 5 212 2m = 5 21 n
2m - 5 21 n = 0
Answer: (1)