9514 1404 393
Answer:
-4.2
Step-by-step explanation:
The linear term is missing from the quadratic, which means it is symmetrical about the vertical line x=0. For each x-intercept greater than 0, another is its opposite. The opposite of 4.2 is -4.2
The other x-intercept is -4.2.
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Consider the parent function ...
y = x^2
which is symmetrical about the y-axis.
Transforming it to ax^2 +k causes it to be scaled vertically by a factor of 'a', and shifted vertically up k units. Neither of these transformations affects the horizontal position of the curve, so it remains symmetrical about the y-axis. Attached is one example of a quadratic of this form with an x-intercept of 4.2.
