We use cookies to personalise content and advertisements and to analyse access to our website. Furthermore, our partners for online advertising receive pseudonymised information about your use of our website. cookie policy and privacy policy.
 
+0  
 
0
721
6
avatar+961 

What is the solution to the equation 15(x3+x2)=-5x24(x3+2)?

 May 13, 2015

Best Answer 

 #6
avatar+27794 
+10

You are right up until the very last step shaniab29544.  On the next to last step you have x3 = 9.  Because the 3 comes after the x we assume this means x to the power 3 (at least that is what heureka and I have assumed), so x-cubed = 9.  This means that x is the cube root of 9 or 3√9.  

If you prefer to interpret this as just x times 3 then we would have x times 3 = 9 so that x would be 9 divided by 3, or x = 3.

.

 May 16, 2015
 #1
avatar+22165 
+10

What is the solution to the equation 1−5(x3+x2)=-5x2−4(x3+2) ?

$$\small{\text{$
\begin{array}{rcl}
1-5(x^3+x^2) &=& -5x^2-4(x^3+2) \\\\
1-5(x^3+x^2) + 5x^2 +4(x^3+2) &=& 0\\\\
1 - 5x^3 - 5x^2 + 5x^2 + 4x^3 + 8 &=& 0 \\\\
-5x^3 - 5x^2 + 5x^2 + 4x^3 + 9 &=& 0 \\\\
-5x^3 \underbrace{- 5x^2 + 5x^2}_{=0} + 4x^3 + 9 &=& 0 \\\\
-5x^3 + 4x^3 + 9 &=& 0 \\\\
-x^3 + 9 &=& 0 \\\\
9 &=& x^3 \\\\
x^3 &=& 9 \qquad | \qquad \sqrt[3]{}\\\\
x &=& \sqrt[3]{9}\\\\
x &=& 2.0800838231
\end{array}
$}}\\\\
\mathbf{ x = 2.0800838231 }$$

.
 May 13, 2015
 #2
avatar+100800 
0

Another beautifully presented answer.  Thank you Heureka  

 May 14, 2015
 #3
avatar+961 
0

it wrong

 May 15, 2015
 #4
avatar+27794 
+5

What makes you think it's wrong shaniab29544?  

 

heureka has given the correct real number root (there are two other roots, but they are complex).

.

 May 15, 2015
 #5
avatar+961 
+10

it like this  i think 

1−5(x3+x2)=-5x2−4(x3+2)1−5x3−5x2=-5x2−4x3−81−5x2=-5x2+x3−89−5x2=-5x2+x39=x3       27=x

 
 May 15, 2015
 #6
avatar+27794 
+10
Best Answer

You are right up until the very last step shaniab29544.  On the next to last step you have x3 = 9.  Because the 3 comes after the x we assume this means x to the power 3 (at least that is what heureka and I have assumed), so x-cubed = 9.  This means that x is the cube root of 9 or 3√9.  

If you prefer to interpret this as just x times 3 then we would have x times 3 = 9 so that x would be 9 divided by 3, or x = 3.

.

Alan May 16, 2015

7 Online Users

avatar