Miscellaneous

Chapter 11 Class 11 - Intro to Three Dimensional Geometry
Serial order wise

### Transcript

Misc 3 If origin is the centroid of the triangle PQR with vertices P (2a, 2, 6), Q (–4, 3b, –10) and R (8, 14, 2c), then find the values of a, b and c. Given Δ PQR where P (2a, 2, 6) , Q (−4, 3b, –10) , R (8, 14, 2c) Also, Origin O (0, 0, 0) is the centroid of Δ PQR We know that Co ordinate of centroid whose vertices are (x1, y1, z1), (x2, y2, z2), (x3, y3, z3) is ((𝑥_1 + 𝑦_1 + 𝑧_1)/3,(𝑥_2 + 𝑦_2 + 𝑧_2)/3,(𝑥_3 + 𝑦_3 + 𝑧_3)/3) Here, x1 = 2a , y1 = 2 , z1 = 6 x2 = – 4 , y2 = 3b , z2 = –10 x3 = 8 , y2 = 14 , z3 = 2c ∴ Coordinates of centroid O(0, 0, 0) (0, 0, 0) = ((2𝑎 + (−4) + 8)/3,(2 + 3𝑏 + 14)/3,(6 + (−10) + 2𝑐)/3) (0, 0, 0) = ((2𝑎 − 4 + 8)/3,(2 + 3𝑏 + 14)/3,(6 − 10 + 2𝑐)/3) (0, 0, 0) = ((2𝑎 + 4)/3,(3𝑏 + 16)/3,(2𝑐 − 4)/3) x – coordinate 0 = (2𝑎 + 4)/3 3(0) = 2a + 4 0 = 2a + 4 2a + 4 = 0 2a = – 4 a = (−4)/2 a = –2 y – coordinate 0 = (3𝑏 + 16)/3 0(3) = 3b + 16 0 = 3b + 16 3b +16 = 0 3b = – 16 b = (−16)/3 z – coordinate 0 = (2𝑐 − 4)/3 3(0) = 2c – 4 0 = 2c – 4 2c – 4 = 0 2c = 4 c = 4/2 c = 2 Thus, a = – 2 , b = (−𝟏𝟔)/𝟑 & c = 2

#### Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.