From the top of a 9 metres high building AB, the angle of elevation of the top of a tower CD is 30º and the angle of depression of the foot of the tower is 60º. What is the height of the tower?  Choose the most appropriate option:
A) 11
B) 12
C) 88
D) 27
E) 10
We have to find the value of CD. We use Sine rule to find the answer easily. Sine rule is aSinA=bSin12=cSinCaSinA=bSin12=cSinC   In triangle 12DE, 9Sin60=xSin309Sin60=xSin30   So 93–√2=x12⇒x=93–√932=x12⇒x=93   In triangle 12CD, CDSin30=93–√Sin60CDSin30=93Sin60   CD12=93–√3–√2⇒CD=3CD12=9332⇒CD=3   So height of the tower = 9 + 3= 
<gadget id="calculator">9 + 3</gadget>
<output>12</output>
12   Answer:12
<result>B</result>
From the top of a 9 metres high building AB, the angle of elevation of the top of a tower CD is 30º and the angle of depression of the foot of the tower is 60º. What is the height of the tower?