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

by AnnaSuxCalc
Tags: inflection, points
P: 55
 Quote by NoMoreExams You would use your calculator and type in arcsin(.618)?
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
 P: 626 OK let's pick a simpler example. If you had to find sin(x) = 1/2 how would you figure out x?
P: 55
 Quote by NoMoreExams OK let's pick a simpler example. If you had to find sin(x) = 1/2 how would you figure out x?
sin-1(1/2) = x
 P: 626 lol sure, but if you didn't have a calculator, how would you figure that one out.
P: 55
 Quote by NoMoreExams lol sure, but if you didn't have a calculator, how would you figure that one out.
oh you got me i dont know
 P: 626 You should go back and review trigonometry. It's on the unit circle.
 P: 55 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 ???
 P: 626 You can look the answer up on wikipedia, it's a common angle and it was already addressed in this thread I believe.
 P: 55 okay Im not sure what your getting at, I know that sin(π/6) = 1/2 and sin(5π/6) = 1/2
 P: 626 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
 P: 55 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?
 P: 626 Well try plugging that into your calculator :)
P: 55
 Quote by NoMoreExams Well try plugging that into your calculator :)
Yay
 P: 626 There you go champ :)
 P: 55 thanks (still didnt tell me your name) :) now i just have to finish the rest of the assignment lol
 P: 626 The beauty of the anonymity of the Internetz ;-)
P: 55
 Quote by NoMoreExams The beauty of the anonymity of the Internetz ;-)
haha okay Genius, thanks for the help
 P: 626 Genius - far, far, far from it but you are welcome.

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