From the top of a 9 metres high building AB, the angle of elevation of the top of a tower CD is 30° and the angle of depression of the foot of the tower is 60°. Find the height of the tower?
a) 9m
b) 18m
c) 20m
d) 27m
e) None of these

• We have to find the value of CD. We use Sine rule to find the answer easily.
  Sine rule is,
  a/Sin A = b/Sin B = c/Sin C
  according to the triangle BDE,
  9/Sin 60 = x/Sin 30
  so x = 9/sqrt(3)
  in triangle BCD,
  CD/Sin 30 =( 9/sqrt(3)) / Sin 60
  which implies CD = 3
  so height of tower is 9 + 3 =12
• 9 years agoHelpfull: Yes(4) No(1)
• We have to find the value of CD. We use Sine rule to find the answer easily. Sine rule is aSinA=bSinB=cSinC
  
  In triangle BDE, 9Sin60=xSin30
  
  So 93√2=x12⇒x=93√
  
  In triangle BCD, CDSin30=93√Sin60
  
  CD12=93√3√2⇒CD=3
  So height of the tower = 9 + 3 = 12
• 9 years agoHelpfull: Yes(2) No(2)
• answer is 18..
  cos60=9/x
  
• 9 years agoHelpfull: Yes(1) No(0)