Question 807877
Parallel lines have equal slope.

Get both equations into slope-intercept form: y = mx + b

L1: x + y = 5
y = (-1)x + 5

L2: Kx + 2y = 0
2y = -Kx
y = (-K/2)x

For the slopes of L1 and L2 to be equal, we must have:
-1 = -K/2

Solve for K:
-1 = -K/2
K/2 = 1
K = 2
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Check the answer: plug-in K = 2 into L2. The slopes of L1 and L2 are both -1.
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