Cumulative Test
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Use process of elimination with the answer choices.
C
In this exercise, we are asked to identify the equation of the given graph. We can see the graph faces downward meaning that the quadratic term of the equation must be negative. Let's start by eliminating answer choices that have positive quadratic terms.
| Answer Choice | Direction | Yes or no? |
|---|---|---|
| A. y=1/2x^2 | Upward | * |
| B. y=2x^2 | Upward | * |
| C. y=-1/2x^2 | Downward | ✓ |
| D. y=-2x^2 | Downward | ✓ |
Now, we have just two answer choices left, let's take a point off the graph and check to see which answer choice it fits.
We can choose any point on the function, let's use ( 2, -2). We want y= -2 when x= 2.
| Answer Choice | x=2 | y | Yes or no? |
|---|---|---|---|
| C. y=-1/2x^2 | y=-1/2( 2)^2 | y = -2 | ✓ |
| D. y=-2x^2 | y=-2( 2)^2 | y = -8 | * |
From this we can see the answer is C.