(4) Use interval notation and inequalities to describe all the slopes for -5≤a≤5. Do the same for the y-intercepts.
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(5) What is the minimum absolute value of the slopes of these lines? At what point on the parabola does this occur? What is this point called?
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(6) Solve the system y=x²,y=2ax-a² to show that, in terms of 'a', the point of intersection of each line and the parabola is (a,a²).
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There are many Common Core objectives here but my primary goal is to provide a simple demo of how to use Desmos to create an interactive exploration.
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This Investigation can be significantly improved with Desmos' New Activity Builder!
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Answers
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(1) x²=6x-9 --> x²-6x+9=0, (x-3)²=0. x=3 is the only solution which shows that (3,9) is the only point of intersection.
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(2) Similar to a tangent line to a circle, y=6x-9 has exactly 1 point of intersection with the curve.
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(3) Slope=2a; y-int= -a²
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(4) -10≤slope≤10 or [-10,10]; -25≤y-int≤0 or [-25,0]
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(5) 0; (0,0); Vertex
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(6) x²=2ax-a² --> x²-2ax+a²=0 --> (x-a)²=0 -->x=a --> y=a²
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