Non-right angled trig.

Aminekhadir · #1 $Old$ December 9th, 2008, 02:09 AM

I tried to solve this question and got the answer to be 79.8 m.
The correct answer is apparrantly 204 m.
I hope you can help me solve this question.

The question:
From point A, the angle of elevation to the top a tall building is 20 degrees. On walking 80 m towards the building the angle of elevation is now 23 degrees. How tall is the building?

Thanks,
Amine

Greengoblin · #2 $Old$ December 9th, 2008, 05:10 AM

You effectively have a right angled triangle split into a smaller right angled triangle, and an irregular triangle. first you can work out the angles inside the iregular triangle.

$180=20+(180-23)+A \implies A=3^{\circ}$

Next you can use the sine rule to find the hypotenuse of the smaller right angled triangle:

$\frac{80}{\sin(3)}=\frac{c}{\sin(20)}\implies c = 522.81m$

then the height of the building h is given by:

$h=522.81\sin(23)=204.3m$

earboth · #3 $Old$ December 9th, 2008, 06:03 AM

Quote:

Originally Posted by Aminekhadir $View Post$

I tried to solve this question and got the answer to be 79.8 m.
The correct answer is apparrantly 204 m.
I hope you can help me solve this question.

The question:
From point A, the angle of elevation to the top a tall building is 20 degrees. On walking 80 m towards the building the angle of elevation is now 23 degrees. How tall is the building?

Thanks,
Amine

Have a look here: http://www.mathhelpforum.com/math-he...879-post2.html

second question.