Quantcast XP Math - Forums - View Single Post - Isolate to solve the equation
View Single Post
Old 04-03-2010   #2

Join Date: Dec 2008
Posts: 249

Originally Posted by magmagod View Post
So the question is basically solve each equation for 0<x<2pi...i just have trouble with isolating the equations for the following:

- square root 2 sinx = 2sinx cos x

- 2cosx - 3/cosx + 2 square root2 = 0

for the first one i got this far:
square root 2 sinx = 2sinx (double angle)
squared both sides and ended with 2 sinx = 4 sin^2x
divided by 2 sinx to both sides and got 1 = 2 sinx
then i isolated for sinx ... sinx = 1/2
is it right so far? then i just found the related acute angle and the values in Q 1 and 3

I appreciate your help so far i will try and help you with your problems..
Wow, these are tough problems the way you have presented them. Maybe you have left out some parentheses or something.

For the 1st one, I am assuming that first dash is NOT a negative sign, therefore:
sinx*sqrt(2) = 2sinxcosx
sqrt(2) = 2cosx
sqrt(2)/2 = cosx
Taking the inverse cos of both sides gives
x = pi/4 and 7*pi/4

If the first dash is a negative sign, then x = 3*pi/4 and 5*pi/4.

Your solution is incorrect because 2sinxcosx = sin2x, not 2sinx.
MAS1 is offline