SOLUTION: I need confirmation on this problem involving factoring: Factor Completely: 16x^4 - 40x^2 + 9 = This is what I came up with: 8(2x^4 - 5x^2) + 1 is this correct? Thanks for

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: I need confirmation on this problem involving factoring: Factor Completely: 16x^4 - 40x^2 + 9 = This is what I came up with: 8(2x^4 - 5x^2) + 1 is this correct? Thanks for      Log On


   



Question 173654: I need confirmation on this problem involving factoring:
Factor Completely: 16x^4 - 40x^2 + 9 =
This is what I came up with:
8(2x^4 - 5x^2) + 1 is this correct? Thanks for any assistance.

Found 2 solutions by nerdybill, Fombitz:
Answer by nerdybill(7384) About Me  (Show Source):
You can put this solution on YOUR website!
16x^4 - 40x^2 + 9 =
This is what I came up with:
8(2x^4 - 5x^2) + 1 is this correct?
.
No
if you expanded your equation:
8(2x^4 - 5x^2) + 1
You would get:
16x^4 - 40x^2 + 1
Which is NOT the same as what you started with.
.
The correct solution is:
16x^4 - 40x^2 + 9
(4x^2-1)(4x^2-9)
.
Can't stop here either because it can be further factored:
(4x^2-1)(4x^2-9)
(2x+1)(2x-1)(2x-3)(2x+3)

Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
No that's not correct.
Let's expand what you got.
8%282x%5E4+-+5x%5E2%29+%2B+1=16x%5E4+-+20x%5E2+%2B+1
Let's try this.
Use a substitution to knock down the degree of the polynomial and hopefully make it look more familiar.
Let u=x%5E2
Now substitute this into your equation.
16x%5E4+-+40x%5E2+%2B+9+=16%28u%5E2%29+-+40u+%2B+9+
16x%5E4+-+40x%5E2+%2B+9+=16u%5E2+-+40u+%2B+9+
Now you have a quadratic equation in u and you can look to factor the right hand side,
16x%5E4+-+40x%5E2+%2B+9=%284u-9%29%284u-1%29
16x%5E4+-+40x%5E2+%2B+9=%284x%5E2-9%29%284x%5E2-1%29
You can further factor the right hand sides,
4x%5E2-9=%282x-3%29%282x%2B3%29
4x%5E2-1=%282x-1%29%282x%2B1%29
.
.
.
16x%5E4+-+40x%5E2+%2B+9=%284x%5E2-9%29%284x%5E2-1%29
16x%5E4+-+40x%5E2+%2B+9=%282x-1%29%282x%2B1%29%282x%2B3%29%282x-3%29