Stephan added 26 new contacts to his phone list. He had to delete 16 old contacts before he could add any more. Stefan now has a
2 answers:
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1. Solve by differentiation (Derivative = 0 at the vertex)
dy/dx= 2x-4
0=2x-4
0=2(x-2)
x=2
when x=2 y=-5
therefore vertex (2,-5)
dy/dx= 2x-4
0=2x-4
0=2(x-2)
x=2
when x=2 y=-5
therefore vertex (2,-5)