Help with related angles (1 Viewer)

[ForbiddenND]

So how do we change any angle to its related first quadrant angle. e.g. 250 to related first quadrant angle. I learnt the ASTC rule but don't know how to apply it to do this lol.

thx for help

 

[Drongoski]

1) you draw the line representing 250 deg (anti-clockwise from the positive x-axis)

2) what angle does it make with the x-axis (for 250 deg it's 70 deg )

3) this then (70 deg) is the related 1st quadrant angle

4) since 250 deg in 3rd quadr. tan +ve and sin & cos -ve.
this means sin 250 = - sin 70; cos 250 = - cos 70 and tan 250 = tan 70

 

[ForbiddenND]

yeah that works but i learnt some random way where its like 180+ , 180- and 360- wahh so confused

 

[youngminii]

It's the same thing.
The positive x axis is 0 OR 360 degrees (since 360 is a full revolution from 0).
The negative x axis is 180 degrees.
Now when you've got 250 degrees, it's 70 degrees below the negative x axis, which is 180 + 70, yes?
When you've got like, 110 degrees, it's 70 degrees above the negative x axis, which is 180 - 70.
For 290 degrees, it's 70 degrees below the positive x axis, which is 360 - 70.
And you've got 70 degrees above the negative x axis, which is 0 + 70.

Your teacher made you rote learn it or something. This is how it actually works. Same thing but.