*HELP* Finding x in [_,_] of Possible Inflection Points

NoMoreExams

You would use your calculator and type in arcsin(.618)?

AnnaSuxCalc

haha, yes I did taht but it only gives me the one value of x, but there are two intersections so there is another value of x that gives sin(x) = 0.6180
if you just do sin^-1 (0.6180) = 0.6662 ---> only one value, i need 2 values

NoMoreExams

OK let's pick a simpler example. If you had to find sin(x) = 1/2 how would you figure out x?

AnnaSuxCalc

sin^-1(1/2) = x

NoMoreExams

lol sure, but if you didn't have a calculator, how would you figure that one out.

AnnaSuxCalc

oh you got me i dont know

NoMoreExams

You should go back and review trigonometry. It's on the unit circle.

AnnaSuxCalc

come on help me out here (your name), lol ok fine soooo...
sinθ = y/r --> y=1 and r=2 using THE theorem x=sqrt3 ???

NoMoreExams

You can look the answer up on wikipedia, it's a common angle and it was already addressed in this thread I believe.

AnnaSuxCalc

okay Im not sure what your getting at, I know that sin(π/6) = 1/2 and sin(5π/6) = 1/2

NoMoreExams

I'm trying to get you to remember how those values were determined. Sin(pi/6) = 1/2 is easy. So we know 30 degrees is what we need. Since we have sine, it's positive in 1st and 2nd quadrants. So in the first quadrant we have 30 degrees, in the 2nd we know our "line" must make a 30 degree angle with the horizontal which would be pi, so we did pi - pi/6 = 5pi/6

AnnaSuxCalc

oh ok so my number is not 1/2 but 0.6180 so that is 38.17degrees
so the line must make a 38.2degree angle with the horizontal since pi is (180degrees)
180-38.2 = 141.2degrees ~2.46rad
is this the answer?

NoMoreExams

Well try plugging that into your calculator :)

AnnaSuxCalc

Yay

NoMoreExams

There you go champ :)

AnnaSuxCalc

thanks (still didnt tell me your name) :) now i just have to finish the rest of the assignment lol

NoMoreExams

The beauty of the anonymity of the Internetz ;-)