Posted by **help!** on Saturday, September 19, 2009 at 2:21am.

Ok, i did this maths trigo question, that says sinx-cos=2/3. I squared it on both sides to get sin2x=5/9 and did the sum. In the end i got two solutions, 16.9 and 73.1. However, when i substituted the answers back into the equation, only one of the 2 answers was correct! The other one didn't work out! Why is this so? I'm pretty sure both answers are correct, so what's going on? Please help!

- Trigo! -
**MathMate**, Saturday, September 19, 2009 at 7:23am
You have done the right step, check your answers after you have squared each side of an equation.

Take a simple case of

x=-4

square both sides,

x²=(-4)²=16

x=√16=±4

check:

x=-4 OK

x=+4 not a solution.

In your case, the solution of 73.126° is correct. The other one is false.

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