How do you write an equation of a line with slope of 3 and contains the point (4, 9)?

2 Answers
Mar 22, 2018

#y=3x-3#

Explanation:

#"the equation of a line in "color(blue)"slope-intercept form"# is.

#•color(white)(x)y=mx+b#

#"where m is the slope and b the y-intercept"#

#"here "m=3#

#rArry=3x+blarrcolor(blue)"is the partial equation"#

#"to find b substitute "(4,9)" into the partial equation"#

#9=12+brArrb=9-12=-3#

#rArry=3x-3larrcolor(red)"is the equation of the line"#

Mar 22, 2018

#y = 3x-3#

Explanation:

You can use the equation of a line in point-slope form:
#y-y_{1} = m(x-x_{1})#

Make the following substitutions:
#x_{1} = 4# (the x-coordinate of the point)
#y_{1} = 9# (the y-coordinate of the same point)
#m = 3# (the slope of the line)

That will give you:
#y-9 = 3(x-4)#

Then simplify:
#y-9 = 3(x-4)#
#y-9 = 3x-12#
#y = 3x-3#