Posted by help! on Saturday, September 19, 2009 at 2:21am.
Ok, i did this maths trigo question, that says sinxcos=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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