Another maths mind blow for an answer

[markymark2406]

Help on this please

 

[bernardgreen]

Help here

https://www.mathsisfun.com/algebra/quadratic-equation.html

 

[JohnW2]

Help on this please

It's difficult to know how to help when the question itself tells you how to do it (there appears to be an unnecessary word "OR" in what is written). I can but presume that you do not really understand what equations are all about, in which case you need to start by reading about that.

Kind Regards, John

 

[Gerrydelasel]

 

[Astra99]

For the equation 10x²-11x-6=0, the roots are 1.5 and -0.4, using the standard formula for the solution of a quadratic (as shown above)

(-(-11) +/- SQR(-11^2 - 4*10*-6))/2*10

(11+/- SQR(121-(-240)) /20

121+240=361
SQR 361=19

11 + 19 = 30
11 - 19 = -8

30/20 = 1.5 ROOT ONE
-8/20 = -0.4 ROOT TWO

QED

It is worth remembering that if (b²-4*a*c) is negative, then the roots are imaginary as the square root of a negative number is imaginary. (That is why we have the "j" operator, where j is -1 LOL)

 

[JohnW2]

<some very correct maths>

As per my initial comment, it would seem that the OP actually needs help in understanding the concept of an equation/formula.

Kind Regards, John

 

[DaveHerns]

What's this got to do with electrics?

 

[JohnW2]

What's this got to do with electrics?

About as much as your question, I'd say

Kind Regards, John

 

[ericmark]

Using excel
=(11-POWER(POWER(11,2)-4*10*-6,0.5))/2*10 answer = -40
=(11+POWER(POWER(11,2)-4*10*-6,0.5))/2*10 answer = +150
I know we need to do this as part of our education on how to use maths, the whole of the electrical theory needs maths, using imaginary numbers is an essential part of understanding AC theory, however it is not some thing which is really required with DIY electrics.

 

[JohnW2]

Using excel
=(11-POWER(POWER(11,2)-4*10*-6,0.5))/2*10 answer = -40
=(11+POWER(POWER(11,2)-4*10*-6,0.5))/2*10 answer = +150

I'm sure the OP did not want to know how to do it with Excel, but, if you're nevertheless going to tell him, you might at least give him the correct answer! ...

=(11-POWER(POWER(11,2)-4*10*-6,0.5))/(2*10) answer = -0.40
=(11+POWER(POWER(11,2)-4*10*-6,0.5))/(2*10) answer = +1.50

... because you forgot those brackets, you multiplied by 10 instead of dividing by 10, hence an error of a factor of 100.

One of the most crucial things to teach about maths, particularly when using software or calculators (or even slide rules), is that one should always look at one's answers and see if, in terms of common sense, those answers 'make sense' - and roots of -40 and 150 do not really make much sense in terms of the equation being solved!

Kind Regards, John

 

[EFLImpudence]

5 and 20 same 100

 

[JohnW2]

5 and 20 same 100

Kind Regards, John

 

[EFLImpudence]

=(11-POWER(POWER(11,2)-4*10*-6,0.5))/(2*10) answer = -0.40
=(11+POWER(POWER(11,2)-4*10*-6,0.5))/(2*10) answer = +1.50

... because you forgot those brackets, you multiplied by 10 instead of dividing by 10, hence an error of a factor of 100.

Should you not have said:
... because you forgot those brackets, you multiplied by 5 instead of dividing by 20?

 

[JohnW2]

Should you not have said: ... because you forgot those brackets, you multiplied by 5 instead of dividing by 20?

Oh, I see.

Whilst that is, indeed, mathematically the same, I think that would have been a confusing way of putting it, since neither 5 nor 20 appear explicitly in the formula being evaluated. The formula requires the 'top part' to be divided by "2a", which is (2 x 10) with our figures. However, without the brackets, eric divided just by the 2 (which, as far as it goes, is correct) and then multiplied the whole lot by 10 (instead of dividing also by the 10).

Whatever, I'm sure that we are agreed, other than about what words to use to describe the error!

Kind Regards, John