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if a and b are the roots of the quadratic equation x^2+4x-k=0 and a>b, find the value of a-b

 Feb 11, 2015

Best Answer 

 #2
avatar+118703 
+5

if a and b are the roots of the quadratic equation x^2+4x-k=0 and a>b, find the value of a-b

[I have replace a with α  and b with   β   because I wanted a and be to stand for the quadratic coefficients]

 

For the quadratic  

 

ax2+bx+c=0Iftherootsareαandβthenα+β=baandα+β=ca

 

 

α+β=4αβ=k(α+β)24αβ=α2+β2+2αβ4αβ=α2+β22αβ=(αβ)2so(αβ)2=(α+β)24αβ(αβ)2=(4)24k(αβ)2=16+4kαβ=±16+4kButαisbiggerthanβsoαβ=16+4kαβ=24+k

 Feb 11, 2015
 #1
avatar+26396 
+5

If a and b are the roots of the quadratic equation x^2+4x-k=0 and a>b, find the value of a-b

 x1,2=4±164(k)2=4±16+4k2=4±4(4+k)2  x1,2=4±24+k2=2±4+k  a=2+4+k|a>b  b=24+k  ab=2+4+k(24+k)=2+4+k+2+4+k)=24+k  ab=24+k 

 Feb 11, 2015
 #2
avatar+118703 
+5
Best Answer

if a and b are the roots of the quadratic equation x^2+4x-k=0 and a>b, find the value of a-b

[I have replace a with α  and b with   β   because I wanted a and be to stand for the quadratic coefficients]

 

For the quadratic  

 

ax2+bx+c=0Iftherootsareαandβthenα+β=baandα+β=ca

 

 

α+β=4αβ=k(α+β)24αβ=α2+β2+2αβ4αβ=α2+β22αβ=(αβ)2so(αβ)2=(α+β)24αβ(αβ)2=(4)24k(αβ)2=16+4kαβ=±16+4kButαisbiggerthanβsoαβ=16+4kαβ=24+k

Melody Feb 11, 2015

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