# solve the equation by an appropriate substitution

• January 12th 2009, 04:26 PM
netlab
solve the equation by an appropriate substitution
solve the equation by making an appropriate substitution

x^4 - 5x^2 + 4 = 0

any help in explaining what needs to be done to solve this question will be appreciated. what substitution are they talking about to be more precise on whats confusing me about this question. (should i just substitute random values for x until i find a solution?)
• January 12th 2009, 04:42 PM
Mush
Quote:

Originally Posted by netlab
solve the equation by making an appropriate substitution

x^4 - 5x^2 + 4 = 0

any help in explaining what needs to be done to solve this question will be appreciated. what substitution are they talking about to be more precise on whats confusing me about this question. (should i just substitute random values for x until i find a solution?)

If you let $y = x^2$, then the equation becomes:

$y^2 - 5y + 4 =0$

Which is a quadratic. Can you solve those?
• January 12th 2009, 04:43 PM
netlab
ok thanks a lot that clears up a lot, and yes i can solve quadratic equations
• January 12th 2009, 05:00 PM
Mush
Quote:

Originally Posted by netlab
ok thanks a lot that clears up a lot, and yes i can solve quadratic equations

No problem.

Just remember that once you have solved for y, you must change the variable back to the original and solve for x!