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Check it out:

m1 = 2 and m2 = -1 / 2

Take the 2 ... Write it as a fraction: 2 / 1

Flip it over: 1 / 2  ... and change the sign: -1 / 2


Let's do a problem:

Let's find the equation of the line that passes through the point
( 1 , 3 ) and is perpendicular to the line 2x + 5y = 4 .

What do we need?

a point

have

a slope

need

STEP 1:  Find the slope

It's perpendicular to 2x + 5y = 4 ...

So, we'll get this guy's slope ...  flip it and change the sign!  Easy!

2x + 5y = 4 ... subtract 2x from both sides of the equation, which gives 5y = -2x + 4 ... y = -( 2 / 5 )x + 4 ... m1 is -2 / 5 ... so, use m2 = 5 / 2