# Sine Rule q

• December 16th 2009, 01:36 PM
Detanon
Sine Rule q
If A = 18degrees, b - a =2, ab =4, using the usual notation fora triangle, use the sine rule to find B.
Help I keep getting this q wrong in my book it says the answer is 53.85, but i keep getting like 53.999.
• December 16th 2009, 01:42 PM
e^(i*pi)
Quote:

Originally Posted by Detanon
If A = 18degrees, b - a =2, ab =4, using the usual notation fora triangle, use the sine rule to find B.
Help I keep getting this q wrong in my book it says the answer is 53.85, but i keep getting like 53.999.

Solve the simultaneous equations for a and b

$a = -1+ \sqrt{5}$ : $b = 1+\sqrt{5}$

$\frac{sinA}{a} = \frac{sinB}{b}$

$B = arcsin \left(\frac{b}{a}sinA\right) = arcsin \left(\frac{1+\sqrt5}{1-\sqrt5}sin(18)\right) =$

How odd, I get -54 exactly
• December 16th 2009, 05:25 PM
Krahl
i get exactly 54.

but thats without rounding. and the book is way off.