Best Answer:
Hi there --

Two things to keep in mind when solving these -- first is how to find the equation of a line, given its slope and point on the line; second how to find the slopes of perpendicular lines.

In this problem, we need to recognize that the slope of x = -2 is undefined, as it's a vertical line. This means that its slope which is generally known to be the negative reciprocals (for defined nonzero numbers) ends up being zero for the case of a line with undefined slope. All this means is that lines perpendicular to a vertical line are always horizontal and, therefore, have slope m = 0.

Given this slope, now derive the equation of the line from slope-intercept form:

y = mx + b,

using m = 0, and the point (2,1) as an instance of x, y -- to find b:

1 = 0*1 + b;

so b = 1.

Thus our equation is y = 0x + 1 or just y = 1.

I put together a short video tutorial which further illustrates this solution, and cited it as a source below. We hope it is helpful.

Source(s):
http://www.youtube.com/watch?v=1GQHGf6z4tU

http://www.purplemath.com/modules/slope2.htm