Mark M. has the correct answer of y = -2x - 1.
I'll add an alternative way to approach the problem. We can assume this is a straight line, so lets look for an equation of the form y=mx + b, where m is the slope and b is the y-intercept (the value of y when x is zero).
We are told the slope, so m is equal to -2. We can write:
y = -2x + b
Now all we need is to find a value of b that forces the line to go through point (2,-5). This is easily done by entering this point into the equation and solving for b:
y = -2x + b
-5 = -2*(2) + b for point (2,-5)
-5 = -4 + b
b = -1
The equation is y = -2x - 1, as Mark M has already deduced.
