What is the value of |-25|?

25

Step-by-step explanation:

|-25| means the absolute value of -25

The absolute value means how far a number is away from zero without consideration of whether or not the number is positive or negative, so the answer would be 25.

The solutions are (0, 4) and (0, -4)

Step-by-step explanation:

Solve this system using substitution:  

Take the negative of the first equation and add the result to the second one:

-x^2 + y^2 = 16 becomes x^2 - y^2 = -16

Then:

x^2    - y^2 = -16

-2x^2 + y^2 = 16

-x^2 = 0, so x must be 0.

By the first equation, if x = 0, -(0)^2 + y^2 = 16, or

y^2 = 16, or y = ±4

The solutions are (0, 4) and (0, -4)