cos(180+A) = -cosA
I did this…
cos180 x cosA - sin180 x sinaA = -cosA
But what do I do next? D:
Cos 180=-1
Sin 180=0
Just wondering, but what grade are you in? I’m not implying you’re unintelligent by this question, I’m just wondering when a student would learn this stuff. I learned it in grade 9, but might be different for everyone.
I’m in 11th grade.
And thank you for your help.
What course?
He wasn’t thanking you Setz.
easy.
cos(a+b) = (cos a)*(cos b)
cos 180=-1 therefore cos(180+A)= (cos 180)(cos A)= -1(cos A)= -cosA
compound angle formulae man, gonna come in handy if you want to do pure maths at a higher level.
I… I never said s/he was?
It’s Pre-Calculus.
When you’re solving trigonometric equations, how do you know which quadrant it’s in?
For example:
2cosx+1=0
I know it’d be cosx=-1/2, but yeah. Maybe it’s easy but I’m stupid and don’t know. D:
I took a Functions and Relations (MCR3U1) course in grade 11; and it was considered pre-calc; is that it?.
To know which quadrant, ask yourself in which part of the quadrant X is negative. If in doubt, draw a circule, draw a big + in the middle to split it into quandrants and look where X is negative :P.
Oooh! Thank you, that’s very helpful! 