Practicing Success
AB is the diameter of a circle with centre O. C and D are two points on the circumference of the circle on either side of AB, such that ∠CAB = 42o and ∠ABD= 57o. What is difference (in degrees) between the measures of ∠CAD and ∠CBD ? |
\({50}^\circ\) \({30}^\circ\) \({10}^\circ\) \({70}^\circ\) |
\({30}^\circ\) |
\(\angle\)ACB = \({90}^\circ\) [as AB is diameter] So, in \(\Delta \)ACB \(\angle\)CBA = \({180}^\circ\) - \(\angle\)ACB - \(\angle\)CAB ⇒ \(\angle\)CBA = \({180}^\circ\) - \({90}^\circ\) - \({42}^\circ\) ⇒ \(\angle\)CBA = \({48}^\circ\) So, \(\angle\)CBD = \(\angle\)CBA - \(\angle\)ABD ⇒ \(\angle\)CBD = \({48}^\circ\) - \({57}^\circ\) ⇒ \(\angle\)CBD = \({105}^\circ\) Again, ADBC is a cyclic quadrilateral So, \(\angle\)CAD = \({180}^\circ\) - \(\angle\)CBD ⇒ \(\angle\)CAD = \({180}^\circ\) - \({105}^\circ\) ⇒ \(\angle\)CAD = \({75}^\circ\) Difference \({105}^\circ\) - \({75}^\circ\) ⇒ \({30}^\circ\) Therefore, the difference (in degrees) between the measures of ∠CAD and ∠CBD is \({30}^\circ\) |