Question

Three wires of length $l_1,l_2,l_3$ form a triangle surmounted by another circular wire, if $l_3$ is the diameter and $l_3=2l_1$ then angle between $l_1$ and $l_3$ will be?

• A. ${30}^o$
• B. ${60}^o$
• C. ${45}^o$
• D. ${90}^o$

Answer 1

Answer: (B)

${60}^o$

we have,

formula,

$\cos \theta =\frac{l_1}{l_3}=\frac{l_1}{2l_1}=\frac{1}{2}$

$\therefore \theta ={\cos }^{-1}\frac{1}{2}={60}^{\circ }$