Homework Help: Math

Posted by Rachel on Friday, January 28, 2011 at 4:09pm.

i) The two lines 4x-6y=-5, and 7x+6y=7 intersect at the point where x= and y=?

ii) If the line 7x+ky=7 is parallel to 4x-6y=-5, then what is the value of k? Answer: k = ?

Math - Reiny, Friday, January 28, 2011 at 4:37pm
The two equations are easy to solve, just add up the two equations and the y term will drop out to get
11x = 2
x = 2/11
sub back into the second (or the first) to get
7(2/11) + 6y = 7
times 11
14 + 66y = 77
66y = 63
y = 63/66 = 21/22

slope of first line = -7/k
slope of 2nd line = 4/6 = 2/3

so -7/k = 2/3
cross-multiply
2k = -21
k = -21/2

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