Showing posts with label Quadratic Form. Show all posts
Showing posts with label Quadratic Form. Show all posts

Wednesday, July 31, 2013

Sunday, July 21, 2013

Can you help me solve for real roots? 2x^8+15x^4=27

u=x^4 
2u^2+15u-27=0 
2u^2+18u-3u-27=0 
2u(u+9)-3(u+9)=0 
(2u-3)(u+9)=0 

but u+9 contributes no real roots 

2u-3=0 
u=3/2 

x^4 = 3/2 

x^2 = +- sqrt(3/2) 

from which we use the principal root 

thus 
%0D%0Ax=++root%284%2C3%2F2%29%0D%0A 
or 
%0D%0Ax=+-+root%284%2C3%2F2%29%0D%0A

Thursday, May 9, 2013

is it possible to write two real numbers whose sum is 4 and whose product is 5?



Your Answer:
y=5%2Fx


%0D%0Ax%2B5%2Fx=5%0D%0A



%0D%0Ax%5E2%2B5=5x%0D%0A


%0D%0Ax%5E2-5x%2B5=0%0D%0A

this is clearly irreducible...so let's use the quadratic formula...


x+=+%28-%28-5%29+%2B-+sqrt%28+%28-5%29%5E2-4%2A1%2A5+%29%29%2F%282%2A1%29+


x+=+%285+%2B-+sqrt%28+5+%29%29%2F2+
So, yes if we extend our search out to all real numbers we can find two irrational numbers that meet our requirements

:)