# Math Help - Non-right angled trig.

1. ## Non-right angled trig.

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

2. 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:

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

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.