# Tips

When solving trigonometric problems, you often don’t have enough time to derive all the formulae from scratch, so it would be useful to learn and memorize the signs of trigonometric functions by quadrants.
But if you are confused or unsure whether the sign is correct, you can have a quick check.

Now:

## If the problem is about the sine of an angle, then:

• imagine a circle,
• the angle formed by radius vector OM and the circle,
• and the sign that the ordinate of point M has, i.e., sign y.

## Like the sine, if the problem is about the cosine of an angle,

• imagine a circle,
• the angle formed by radius vector OM and the circle,
• and the sign that the abscissa of point M has, i.e., sign x.

The signs of sine

The signs of cosine