Question

−13π/5 find the reference angle

Answer 1

I would convert to degrees first seems to make it easier.

`(-13 \pi )/(5)`×
`(180)/( \pi )`
= -468
by adding 360 twice we get the coterminal angle 252

252 is in the 3rd quadrant so 180 is the closest angle on the x-axis
ref angle = 252 - 180 = 72

If necessary convert back to radians...
`72( ( \pi )/(180) )= (2 \pi )/(5)`