If the line segment joining the points $A(a,\,b)$ and $B(c,\,d)$ subtends an angle $ heta $ at the origin, then $\cos heta $ is equal to

Question

If the line segment joining the points $A(a,\,b)$ and $B(c,\,d)$ subtends an angle $	heta $ at the origin, then $\cos 	heta $ is equal to

Accepted Answer

$\frac{ac+bd}{\sqrt{({{a}^{2}}+{{b}^{2}})\,({{c}^{2}}+{{d}^{2}})}}$

Answer

$\frac{ab+cd}{\sqrt{({{a}^{2}}+{{b}^{2}})\,({{c}^{2}}+{{d}^{2}})}}$

Answer

$\frac{ac-bd}{\sqrt{({{a}^{2}}+{{b}^{2}})\,({{c}^{2}}+{{d}^{2}})}}$

Answer

None of these

trigonometry