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x2-3x-10<0

 Feb 26, 2015

Best Answer 

 #1
avatar+118723 
+5

$$x^2-3x-10<0$$

 

The easiest way to do these is to think of a the parabola   

$$y=x^2-3x-10\\$$

 

The above inequality will be true when y is negative.  i.e. the parabola is under the x axis.

This is a concave up parabola because the coefficient of x^2 is positive

So we will need to solve 

$$\\x^2-3x-10=0\\
(x-5)(x+2)=0\\
x=5,\;\;x=-2\\$$

since the paraola is concave up, the bit under the x axis is between these two roots.

so

$$\\x^2-3x-10<0\\
When\;\;-2

 Feb 27, 2015
 #1
avatar+118723 
+5
Best Answer

$$x^2-3x-10<0$$

 

The easiest way to do these is to think of a the parabola   

$$y=x^2-3x-10\\$$

 

The above inequality will be true when y is negative.  i.e. the parabola is under the x axis.

This is a concave up parabola because the coefficient of x^2 is positive

So we will need to solve 

$$\\x^2-3x-10=0\\
(x-5)(x+2)=0\\
x=5,\;\;x=-2\\$$

since the paraola is concave up, the bit under the x axis is between these two roots.

so

$$\\x^2-3x-10<0\\
When\;\;-2

Melody Feb 27, 2015

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