Solve by completing the square:
1 answer:
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Answer:
A
Step-by-step explanation:
The velocity of a moving body is given by the equation:
Is the velocity is <em>positive </em>(v>0), then our object will be moving <em>forwards</em>.
And if the velocity is negative (v<0), then our object will be moving <em>backwards</em>.
We want to find between which interval(s) is the object moving backwards. Hence, the second condition. Therefore:
By substitution:
Solve. To do so, we can first solve for <em>t</em> and then test values. By factoring:
Zero Product Property:
Now, by testing values for t<1, 1<t<4, and t>4, we see that:
So, the (only) interval for which <em>v</em> is <0 is the second interval: 1<t<4.
Hence, our answer is A.