In the right-angled triangle below, is it possible to find length $BC$ with only length $AC$ and angle $A$?

triangle rectangle

  • 1
    $\begingroup$ $BC=(AC)f(A)$, where $f$ is one of the basic trig functions. I'll leave you to work out which one. $\endgroup$ – David May 25 '18 at 1:36
  • $\begingroup$ "Triangle rectangle" was a new phrase to me. It makes perfect sense (at least once I see the picture), but it's more common in English to use the less latin-ified "right-angled triangle". $\endgroup$ – Arthur May 25 '18 at 1:58
  • $\begingroup$ Thanks, I translated literally I didn't know the english term. $\endgroup$ – Manspider May 25 '18 at 2:38

You know Angle A and side length AC therefore to find side length BC you can use trigonometry.

$\tan\theta = \frac O A$
$\tan A = \frac{BC}{AC}$
$BC=\tan A\times AC$


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