# Rearrange Acos equation for b

Apologies for what is probably an easy question but my mind has gone black, I need to rearrange this equation for $b$: $$a=\left(\frac{180}{\pi}\right)\arccos \left(\frac{b-cd}{b}\right)$$

\begin{align*} a &= \frac{180}{\pi}\arccos\frac{b-cd}{b}\\ \arccos\left(1-\frac{cd}{b}\right) &= \frac{a\pi}{180}\\ 1-\frac{cd}{b} &= \cos\frac{a\pi}{180}\\ \frac{cd}b &= 1-\cos\frac{a\pi}{180}\\ b &= \frac{cd}{1-\cos\frac{a\pi}{180}} \end{align*}
• Was it originally an $\arccos$ in the inital question or $\cos$ multiplied by a constant $A$? Nov 13, 2014 at 15:28
• I also would like @bolt19 to confirm. The above was based on how WolframAlpha interpreted a = Acos((b - (c * d)) / b) * 180 / PI Nov 13, 2014 at 15:31