MHB Show that the solution is not suitable....

[mathlearn]

Data

The solution of the quadratic equation $5x^2-5x-11=0$ is $x=\frac{5-7\sqrt{5}}{10}$

PB=$2x-1$ cm

Where do I need help

By substituting the solution $x=\frac{5-7\sqrt{5}}{10}$ in the expression above for the length of $PB$ , show that this solution is not suitable.

Many Thanks :)

 

[MarkFL]

What kind of number cannot represent a physical measure?

 

[mathlearn]

What kind of number cannot represent a physical measure?

A fraction or a decimal :)

 

[MarkFL]

A fraction or a decimal :)

No...what's the formula for the distance between two numbers on a number line?

 

[mathlearn]

No...what's the formula for the distance between two numbers on a number line?

(Thinking) I'm sorry i don't know

 

[MarkFL]

Suppose that $p$ and $q$ are two real numbers. Then the distance $d$ between these numbers, given in units, on a real number line is:

$$d=\sqrt{(p-q)^2}=|p-q|$$

So, what is the range of values we can get for $d$?

 

[mathlearn]

Suppose that $p$ and $q$ are two real numbers. Then the distance $d$ between these numbers, given in units, on a real number line is:

$$d=\sqrt{(p-q)^2}=|p-q|$$

So, what is the range of values we can get for $d$?

My Apologies MarkFL , I don't know that either (Doh)

 

[I like Serena]

What kind of number cannot represent a physical measure?

A fraction or a decimal :)

I think we can measure 1/6 of an inch, or 0.12 cm, can't we?
But a length cannot be negative... (Thinking)

 

[mathlearn]

I think we can measure 1/6 of an inch, or 0.12 cm, can't we?
But a length cannot be negative... (Thinking)

Agreed (Nod) Now what is meant above is that as $x$ obtained by simplifying the quadratic equation is negative It is not suitable?...(Thinking)

 

[Greg]

PB=$2x-1$ cm

By substituting the solution $x=\frac{5-7\sqrt{5}}{10}$ in the expression above for the length of $PB$ ...

After doing that, what do you find?

 

[mathlearn]

After doing that, what do you find?

Yeah why not simplify it (Sun)

With PB=$2x-1$ given,

$2*\frac{5-7\sqrt{5}}{10}-1$

$\frac{5-7\sqrt{5}}{5}-1$

$\frac{5-7\sqrt{5}}{5}-\frac{5}{5}$

$\frac{-7\sqrt{5}}{5}$