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Given that line AB is tangent to the circle, find m

Given that line AB is tangent to the circle, find m-example-1
User FlyC
by
2.6k points

1 Answer

21 votes
21 votes

Solution:

Given the figure below:

To solve for m∠CAB, we use the chord-tangent theorem which states that when a chord and a tangent intersect at a point, it makes angles that are half the intercepted arc.

Thus,


m\angle CAB=(1)/(2)* arc\text{ CDB}

where


\begin{gathered} m\angle CAB=(4x+37)\degree \\ arc\text{ CDB=\lparen9x+53\rparen}\degree \end{gathered}

By substituting these values into the above equation, we have


4x+37=(1)/(2)(9x+53)

Multiplying through by 2, we have


\begin{gathered} 2(4x+37)=(9x+53) \\ open\text{ parentheses,} \\ 8x+74=9x+53 \end{gathered}

Collect like terms,


\begin{gathered} 8x-9x=53-74 \\ \Rightarrow-x=-21 \\ divide\text{ both sides by -1} \\ -(x)/(-1)=-(21)/(-1) \\ \Rightarrow x=21 \end{gathered}

Recall that


\begin{gathered} m\operatorname{\angle}CAB=(4x+37)\operatorname{\degree} \\ where \\ x=21 \\ thus, \\ m\operatorname{\angle}CAB=4(21)+37 \\ =84+37 \\ \Rightarrow m\operatorname{\angle}CAB=121\degree \end{gathered}

Hence, the measure of the angle CAB is


121\degree

Given that line AB is tangent to the circle, find m-example-1
User Kiran Vemuri
by
3.1k points