The Total solution for NCERT class 6-12
If the line segmentjoining the points P(x1,y1) and Q(x2, y2) subtends an angle α at the origin O, prove that: OP. OQ cos α = x1 x2 + y1 y2.
Given,
Two points P and Q subtends an angle α at the origin as shown infigure:
From figure we can see that points O, P and Q forms a triangle.
Clearly in ΔOPQ we have: