A line has a slope of #-2# and includes the points #(-1, -4)# and #(d, -8)#. What is the value of #d#?

2 Answers
Bhavin B.
May 2, 2018

#d=1#

Explanation:

from standard equation of line which is #y=mx+c#, m is the slope of the line.
So from the data given, we get:
#y=-2x+c#
from point (-1,-4), we can find the value of c:
#-4 = -2(-1)+c#
#-4 = 2+c#
#-4-2=c#
#c=-6#
Now the line equation becomes:
#y=-2x-6#
Now, we use the point (d,-8) to find value of d:
#-8 = -2d-6# (x = d)
#-8+6=-2d#
#-2=-2d#
#-(2/2)=d#
#d=1#

Jim G.
May 2, 2018

#d=1#

Explanation:

#"calculate the slope m using the "color(blue)"gradient formula"#

#•color(white)(x)m=(y_2-y_1)/(x_2-x_1)#

#"let "(x_1,y_1)=(-1,-4)" and "(x_2,y_2)=(d,-8)#

#rArrm=(-8-(-4))/(d-(-1))=(-4)/(d+1)#

#"we are given "m=-2" thus equating gives"#

#(-4)/(d+1)=-2#

#rArr-2(d+1)=-4#

#rArr-2d-2=-4#

#rArr-2d=-4+2=-2#

#rArrd=(-2)/(-2)=1#

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