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Find all values of p such that2(x+4)(x-2p)has a minimum value of -18.

 

Please write in latex form, so that i can write it myself. Do not put those complicated parts.

 Nov 1, 2014

Best Answer 

 #1
avatar+33665 
+5

$$f(x,p)=2(x+4)(x-2p)$$

 

Differentiate with respect to x

$$\frac{df(x,p)}{dx}=4x-4p+8$$

 

Set this equal to zero to find the value of x in terms of p at the minimum

$$4x-4p+8=0 \Rightarrow x=p-2$$

 

Put this value of x back into the f(x,p), set the result equal to -18 and solve for p

$$2(p-2+4)(p-2-2p)=-18$$

$$(p+2)^2=9$$

$$p+2=\pm3$$

 

so p = 1 and p = -5

.

 Nov 2, 2014
 #1
avatar+33665 
+5
Best Answer

$$f(x,p)=2(x+4)(x-2p)$$

 

Differentiate with respect to x

$$\frac{df(x,p)}{dx}=4x-4p+8$$

 

Set this equal to zero to find the value of x in terms of p at the minimum

$$4x-4p+8=0 \Rightarrow x=p-2$$

 

Put this value of x back into the f(x,p), set the result equal to -18 and solve for p

$$2(p-2+4)(p-2-2p)=-18$$

$$(p+2)^2=9$$

$$p+2=\pm3$$

 

so p = 1 and p = -5

.

Alan Nov 2, 2014

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