Signs of trig functions

Before solving a trig equation, need look at the sign of the equation, AND identify which one or multiple quadrants will the solutions land in.

• Quadrant I: All trig functions are POSITIVE.
• Quadrant II: Only sin(x) is POSITIVE, others are all NEGATIVE.
• Quadrant III: Only tan(x) is POSITIVE, others are all NEGATIVE.
• Quadrant IV: Only cos(x) is POSITIVE, others are all NEGATIVE.

e.g.
sin(x) = 123 have a positive sign, so it will have two solutions: one in Quadrant I, another be Quadrant II.
-cos(2x+3)=234have a negative sign, so it'll have two solutions in Quadrant IIand Quadrant III.