MAth problem(cos, sin)

[DDSelin2mori]

Advertisement - Members don't see this ad

I have problem in finding the cos or sin of the angles more than 90. I would appropriate if someone explain it to me. For example is this true: sin 120= sin(180-120)=sin 60, but for Cos(120)=cos (180-120)=-Sin 60... so for cos it would always change to Sin? How about tan and cot?

 

[bigstix808]

there is just wayyyy too much for one person to explain what you are asking. but know your basics (sin= O/H; cos= A/H; tan= O/A) and you should pretty much be able to plug-and-play all the other stuff you're asking.

oh yea, look at this pic. there is a plethera of information on it 😀
(cos = x-coordinate; sin = y-coordinate) <--NOT a universal rule BTW, just makes this pic easier to read

notice the sign changes in each quadrant, that is key for what you are asking

 

[joh020340]

A trick I learned dealing with angles above 90 was this. Whatever quadrant it is in, find the angle it makes with the x axis: be it the positive of negative direction, it doesn't matter. Then to determine if it is a positive number you can remember this. All Seniors Take Calculus. (I learned this in high school). All means all (sin, cos, tan) are positive in quadrant I. Seniors mean sin is positive in quadrant II. Take means tan is positive in quadrant III. Calculus means cos is positive in quadrant IV. It works good enough for me. Otherwise you could draw the angle and see that one side is + and the other is - so it must be - overall. Whatever works.

 

[doc3232]

The trick is to visualize that circle 2 posts above me every time you do such problems, they are confusing for all of us until we visualize that circle, then its very easy.

 

[DDSelin2mori]

there is just wayyyy too much for one person to explain what you are asking. but know your basics (sin= O/H; cos= A/H; tan= O/A) and you should pretty much be able to plug-and-play all the other stuff you're asking.

oh yea, look at this pic. there is a plethera of information on it 😀
(cos = x-coordinate; sin = y-coordinate) <--NOT a universal rule BTW, just makes this pic easier to read

notice the sign changes in each quadrant, that is key for what you are asking

This is really helpful. Thank u so much