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I need help solving the following:

 

35-b^2=2b

 

Which is shortened alot already, but I can't seem to find a way to continue on the equation?

 

The Web.2.0calc.com calculator only gives me the answer, which is not intresting. I need to know HOW to solve this!

 

Thanks, Best Regars, Mormert.smiley

 Sep 27, 2016

Best Answer 

 #2
avatar+36916 
+5

....or you can just factor it:

35-b^2 = 2b          add  'b^2 - 35 ' to both sides

0=b^2 + 2b - 35

(b+7)(b-5) = 0        Now either  b+7   or  b-5  (or both) = 0   so b = -7 or 5

 Sep 27, 2016
 #1
avatar+14915 
+10

Hello, good morning Mormert!

 

35-b^2=2b      b = ?

 

The general form of a quadratic equation is

ax² + bx + c = 0

 

x is calculated using the equation solution

\({\color{Blue}x = {-b \pm \sqrt{b^2-4ac} \over 2a}}\)

 

Put the equation in the general form.

 

35-b²=2b

-b² - 2b + 35 = 0          Replacing b = x

-x² - 2x + 35 = 0

ax² + bx + c = 0

a=-1  b=-2  c=35

\({\color{Blue}x = {-b \pm \sqrt{b^2-4ac} \over 2a}}\)

\({\color{Blue}x = {-(-2) \pm \sqrt{(-2)^2-4*(-1)*35} \over 2*(-1)}}\)

 

\({\color{Blue}x=\frac{2\pm \sqrt{144} }{-2} = \frac {2\pm12}{-2}}\)

 

x1 = - 7

x2 = 5            

Swap back x b

b1 = - 7

b2 = 5              laugh !

 

I hope I could help you.

 

asinus: -)laugh!

 Sep 27, 2016
edited by asinus  Sep 27, 2016
 #2
avatar+36916 
+5
Best Answer

....or you can just factor it:

35-b^2 = 2b          add  'b^2 - 35 ' to both sides

0=b^2 + 2b - 35

(b+7)(b-5) = 0        Now either  b+7   or  b-5  (or both) = 0   so b = -7 or 5

ElectricPavlov Sep 27, 2016
 #3
avatar+130 
0

Thanks for the help!

 

I think I will understand this better later on since I am only in 1st grade in upper secondary school (gymnasium), and we have'nt gone through this stuff yet. But it was an exercise in the book...

 

Cheers ^^ :D

 Sep 27, 2016

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