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find the value of k so that the lines whose equations are 3x₊6ky=7 and 9x₊8y=15 are parallel.

Sagot :

to have the lines parallel they must have the same slope.
getting the slope of the second equation you'll have:
9x + 8y = 15
having it the slope-intercept form, y=mx+b where m is the slope you'll have:
8y = 15 - 9x 
y = -9x/8 + 15/8
y = (-9/8)x + 15/8
slope, m=-9/8
from the first equation 
3x + 6ky = 7
6ky = -3x + 7 
y = -3x/6k + 7/6k
the slope is (-3x)/6k
equating the slope of the two equations you'll have:
[tex] \frac{-9}{8} = \frac{3}{6k} [/tex]
cross multiply
-9(6k) = 3(8)
-54k = 24
k = -24/54
k = -4/9