For any two points M and N in the XY-plane, let MN denote the vector from M to N, and 0 denote the zero vector. Let P, Q and R be three distinct points in the XY-plane. Let S be a point inside the triangle PQR such that SP + 5 SQ + 6 SR = 0. Let E and F be the mid-points of the sides PR and QR, respectively. Then the value of length of the line segment EFlength of the line segment ES is .
Answer
1.15 to 1.25
Solution
With position vectors p, q, r, s: ( p - s) + 5( q - s) + 6( r - s) = 0 s = p + 5 q + 6 r12.
e = p + r2, f = q + r2, so EF = q - p2 and EF = PQ2.
ES = p + 5 q + 6 r12 - 6 p + 6 r12 = 5( q - p)12, so ES = 5PQ12.
EFES = 1/25/12 = 65 = 1.2.
Answer: 1.2