1)Solve this equation: x+√(x^2+4/x^2 +4)=4
2)a, b and c are the sides of a triangle and p , q are positive numbers and p+q = 1 . Prove that pa^2+qb^2≥pqc^2.
3)a and b are real positive numbers. a^n=a+1 and b^2n=b+3
n ∈N and n >1. Compare a with b.
Let c be the hypotenuse, since it is the longest side of a triangle, and therefore the greatest number.
Then by Pythagoreans theorem,
We can substitute into our equation:
Now we know that p and q are between zero and one, thus pq < p and pq < q
Which means that:
So we can say that there are values which are greater than zero, where:
Now substituting these values into our equation:
And subtracting from both sides we get
Since are greater than zero, their sum is greater than zero:
but this contradicts that they equal zero.
So our assumption that is greater than must be incorrect.
Therefore is not greater than
So must be either less than or equal to
I graphed the first one, and found that x=1 is also a solution, I don't know how to find it mathematically, though, except with Newton's method.
Okay, I got it.
Now there is a formula, I think it was Gauss who found it, but it's been a few semesters so I can't remember it exactly. It says something along the lines of:
If you have a polynomial, and p is one of the factors of the coefficient of the first term (so I guess that would be ), and q is a factor of the coefficient of the second term (so ) then if there is a factor, it will take the form of
In this case, lets use q/p, where q=1 and p=2
then I did long division (I forgot how to do short division >.<)
So is a factor, giving us
So x= -.5 or x=1
1) Solve: .
We have: .
Square both sides: .
We find that is a root.
The cubic factors: .
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Did anyone notice that the radical contains a perfect square?
We have: .
Then: . . . . which yields the two roots above.
nice use of LaTeX here!
(i wonder if i can improve on the code, maybe not. but there must be a way of not using so many arrays)
Well, okay, I do!I noticed that the terms were squares, but I didn't see they were a perfect square,
I don't have enough exposure to unusual formats. . . . . Who does?
To tell the truth, I learned about these interesting forms during Calculus
. . while working with Arc Length problems.
The arc length formula is: .
We must take the derivative of the function, square it, add one, and take the square root.
. . Then we must integrate this ugly function.
If the problem's author is humane, the expression simplifies very nicely.
However, by necessity, the original function is usually strange-looking.
Here's an example: .
(Seriously, who would want to graph that curve anyway
. . and find the length of a portion of it?)
We have: .
Then: . .
. . which looks like  except for a sign-change.
Hence, we are expected to recognize it as: .
And now we can integrate: .
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If you haven't had Calculus yet, it's still an interesting bit of algebra.
It's a great reputation-maker.
Glance at and say: .Obviously, it's
. . and ride off into the sunset.
Blertta, I don't know if you saw this, but I got problem #2 in post 5: http://www.mathhelpforum.com/math-he...513-post5.html