Find k such that the line is tangent to the graph of the function.

Question

Function	Line	f(x) = k	x
	y = 2x + 18

k = 

Answer 1

desmos.com/calculator/qjz9bql1so

Answer 2

y=k√x +> dy/dx=k/[2√x]

dy/dx = 2 when k/√x=4, i.e. x=k²/16 and at that point y=k²/4

2x+18 must pass through the point (k²/16,k²/4)

k²/4 = 2k²/16 + 18

4k² = 2k² + 16*18

2k² = 16*18

k=12