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Let \(f(x)=(2x+1)(x-3)-2x^2+4x\).
a) Simplify the expression and write \(f(x)\) in the form \(mx+b\).
b) Find \(f(-5)\), \(f(-3)\), \(f(0)\), and \(f(2)\).
c) Determine algebraically whether \(P(12, -15)\) lies on the graph.
Hints
- Expand the product, then combine the \(x^2\)-terms, x-terms, and constants.
- Substitute each input into the simplified expression.
- A point lies on the graph when its coordinates satisfy the equation.
Solution
1. Expand and combine like terms:
\(f(x)=2x^2-6x+x-3-2x^2+4x=-x-3\).
2. \(f(-5)=5-3=2\), \(f(-3)=3-3=0\), \(f(0)=-3\), and \(f(2)=-2-3=-5\).
3. \(f(12)=-12-3=-15\), which matches the y-coordinate of \(P\). Therefore, \(P\) lies on the graph.
Answer
a) \(f(x)=-x-3\)
b) \(f(-5)=2\), \(f(-3)=0\), \(f(0)=-3\), \(f(2)=-5\)
c) Yes.
