According to the definition: the sine value of an angle is the abscissa of the intersection of this angle and the unit circle.

The cosine of an angle is the ordinate of the intersection of an angle and the unit circle, and all angles intersect the unit circle, so there are sine and cosine values.

All acute angles have tangents.

Individual angles have no tangent: for example, k π+90 (π is pie 3.1415926535 ...) k = z.

At this time, the abscissa of the intersection of the terminal edge of the angle and the unit element is 0,

According to the definition, the ordinate of the intersection of the terminal edge of Tan x = X and the unit cell: the abscissa of this point.

The abscissa 0 cannot be used as a divisor, so there is no tangent value.

Of course, the point on the coordinate system (1, 0) can also be used as a straight line of the l⊥x axis, and this line is called the tan line (tangent).

Once the angle (y) passing through the origin and this line have the intersection point a, then tan y = xa: ya (abscissa of a: ordinate of a).

In fact, as above, when the terminal edge of the angle and the tangent line do not intersect (that is, they are parallel to each other)

It is easy to get that this angle is kπ+90 (π is pie 3.1415926535 ...) k = z.

So the acute angle must have a tangent value.

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