Find and angle between 0 and 2pi that is coterminal with the angle given by - 77pi/5

**mathstupid** · April 15th 2009, 10:39 PM

find an angle between 0 and 2pi that is coterminal with the angle given by -77pi/5

thanks! much appreciated

**Twig** · April 15th 2009, 11:17 PM

$\frac{-77 \pi}{5} = -15 \pi -\frac{2 \pi}{5}$

Angle coterminal with $-\frac{2 \pi}{5} \mbox{ is } \frac{8 \pi}{5}$

**mathstupid** · April 16th 2009, 12:08 AM

sorry but can you explain that a bit because my math teacher is really picky about the work we show.

shouldnt it be:

-77pi/5 + 2pi + 2pi + 2pi + 2pi + 2pi + 2pi + 2pi + 2pi = 3pi/5 ?

**Twig** · April 16th 2009, 08:45 AM

oops, yeah sry, $\frac{3\pi}{5}$ is right.

$\frac{-77\pi}{5} = -15\pi -\frac{2\pi}{5}$ (You can check this).

Now $-15\pi$ is "being at the same place" as just $\pi$ .

So being at pi, $\frac{5\pi}{5} - \frac{2\pi}{5} = \frac{3\pi}{5}$

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