Question

What is the equation of a line that is perpendicular to −x+2y=4 and passes through the point (−2, 1) ? Enter your equation in the box

Answer 1

Perpendicular lines have slopes that multiply to get -1
y=mx+b is the slope intercept equation
m=slope

so get into y=mx+b form
-x+2y=4
solve for y
add x both sides
2y=x+4
divide by 2 both sides
y=(1/2)x+2
the slope is 1/2

perppendicular line slope multiplies to -1
1/2 times what=-1
times 2/1 both sides
what=-2/1=-2

y=-2x+b
find b
we are given a point is (-2,1)
when x=-2, y=1
1=-2(-2)+b
1=4+b
minus 3 both sides
-3=b

so the equation is
y=-2x-3

your teacher might want it in standard form (ax+by=c) so
add 2x both sides
2x+y=-3 is an equation


so y=-2x-3 is correct (slope intercept form)
2x+y=-3 is also correct (standard form)