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#1 2007-10-22 00:48:22

Daniel123
Member
Registered: 2007-05-23
Posts: 663

Inequalities

a) Use algebra to find the set of values of x for which x(x-5) > 36
b) Using your answer to part a, find the set of values of y for which y²(y²-5) > 36

Thanks.

Last edited by Daniel123 (2007-10-22 00:49:06)

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#2 2007-10-22 00:54:22

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

Re: Inequalities

x(x-5)>36
x² - 5x - 36 > 0
(x-9)(x+4) > 0.

Drawing a sketch of the graph shows that the solution to the inequality is then x<-4 or x>9.

For the second part, we now need to find values of y such that y²<-4 or y² >9.

Squares are never negative, so nothing will fit the first part. y² > 9 can be solved though, and has the solution y<-3 or y>3.

(Or, if you want to be clever, |y|>3.)


Why did the vector cross the road?
It wanted to be normal.

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#3 2007-10-22 01:00:01

Daniel123
Member
Registered: 2007-05-23
Posts: 663

Re: Inequalities

aah, it was the y²<-4 that threw me. Thanks.

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