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OpenStudy (liv1234):
OpenStudy (vishweshshrimali5):
The correct method:
1. Find out dy/dx
2. Put dy/dx = 0 and solve for x
3. Find out d^2 y/dx^2 ...
4. Put the values of x you obtained from step 2 in expressions from step 3
5. If d^2 y/dx^2 < 0 => Maximum at that point; if d^2 y/dx^2 > 0 => Minimum at that point... I won't go deep into d^2 y/dx^2 = 0
OpenStudy (liv1234):
Would the answer be C?
OpenStudy (vishweshshrimali5):
dy/dx = -2x + 4 = 0 => x = 2
d^2 y/dx^2 = -2
At x = 2, d^2 y/dx^2 < 0 => Maximum
y @ x = 2 is -4 + 8 - 4 = 0
So you are partially correct.. the correct answer is A
OpenStudy (liv1234):
Okay, thank you! Can you help me with a similar question, please?
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OpenStudy (vishweshshrimali5):
Sure
OpenStudy (liv1234):
OpenStudy (vishweshshrimali5):
What do you think?
OpenStudy (vishweshshrimali5):
What is dy/dx here?
OpenStudy (liv1234):
I think B
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OpenStudy (vishweshshrimali5):
Nope
OpenStudy (vishweshshrimali5):
How did you get it?
OpenStudy (liv1234):
Ohh wait, I was looking at the question wrong!
OpenStudy (liv1234):
Can you give me a hint?
OpenStudy (vishweshshrimali5):
Yeah sure
First find out dy/dx... You will get dy/dx = x + 8
Put it equal to 0, find out the value of x
Then find out d^2y/dx^2
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OpenStudy (liv1234):
Ohh would it be C? Because 8-8=0?
OpenStudy (vishweshshrimali5):
Wait what is d^2y/dx^2 ?
OpenStudy (liv1234):
I'm not sure.
OpenStudy (vishweshshrimali5):
Okay can you find out x from dy/dx = 0 ?
OpenStudy (liv1234):
No, I'm confused on what dy/dx is
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OpenStudy (vishweshshrimali5):
You have done calculus right?
OpenStudy (liv1234):
No. I'm only in Algebra 2.
OpenStudy (vishweshshrimali5):
Oops!! My mistake then...
OpenStudy (vishweshshrimali5):
Okay so we have another option...|dw:1459349375053:dw|
OpenStudy (vishweshshrimali5):
Now the above was the graph when a is positive
When a is -ve the graph becomes:
|dw:1459349456360:dw|