John N. answered 09/26/19
High school math teacher, here to help with any math problem!
There are 2 things you need to write an equation of a line: slope and y-intercept. In the equation given, the slope is 2/5. To find a perpendicular slope, you find the "opposite reciprocal", which means "flip and change the sign". With that said, your perpendicular slope is -5/2.
Using the perpendicular slope (m) and the ordered pair (x, y), plug those into y=mx+b and solve for b, which looks like this:
y=mx+b >>> -4=(-5/2)*(2)+b
Then use order of operations and properties of equations to solve for b:
-4=(-5/2)*(2)+b >>> -4=-5+b >>> 1=b. Your y-intercept is 1.
Finally, take your perpendicular slope and y-intercept and put it into y=mx+b. Your answer is:
y = -5/2 x + 1