Using the unit circle, you can visualise the secant as follows:
- Draw the vertical line passing trough (1,0)
- Extend the radius until it meets this line at point P
- The length of OP is the secant of your angle.
Since -90 means that the radius points downwards, it means that the radius is vertical as well, and thus it never meets the vertical line through (1,0).
Thus, the secant is not defined at -90.
In fact, if we switch back to the function notation, we can confirm this claim, since we have

which is undefined.
X+y=18
5x+y=62
x is number of five dollar bills and y is one dollar bills.
The question didn't make sense, could you add more to it?
A geometry app shows lengths that add up to 27.4 units.
The Pythagorean theorem can be used to find the lengths of the segments. Each length is the square root of the sum of squares of the difference in x-coordinates and the difference in y-coordinates.
segment AB: length = √(3²+8²) = √73 ≈ 8.544
segment BC: length = √(7²+4²) = √65 ≈ 8.062
segment CA: length = √(10²+4²) = √116 ≈ 10.770
Then the total perimeter is the sum of these lengths:
... 8.544 +8.062 +10.770 = 27.376 ≈ 27.4 . . . . units
123 - Use PEMDAS but since you have both division and multiplication you can just go from left to right