please solve (1 Viewer)

brownie46 · Oct 13, 2015

y4-15y²-44=0 find y

sharoooooo · Oct 13, 2015

use the quadratic formula.
answer

InteGrand · Oct 13, 2015

brownie46 said:
y4-15y²-44=0 find y

$$y^4 - 15y^2 - 44 = 0$.$

$By the quadratic formula, $y^2 = \frac{15\pm \sqrt{15^2 +4\times 44}}{2}$.$

$Since $y^2 \geq 0$ for real $y$, we have $y^2 = \frac{15 +\sqrt{15^2 + 4\times 44}}{2}=\frac{15+\sqrt{401}}{2}$.$

$Hence $y=\pm \sqrt{\frac{15+\sqrt{401}}{2}}$ for real solutions.$

ashaaaa · Oct 14, 2015

I did it a different way. I did:

y^4 - 15y^2 - 44 = 0

let y^2 = u

u^2 - 15u - 44 = 0

(u-11)(u-4) = 0

Therefore, u = 11 or u = 4

Sub that back into y^2 = u

y^2 = 11 or y^2 = 4

Therefore y = square root of 11 or y = square root of 4

InteGrand · Oct 14, 2015

ashaaaa said:
I did it a different way. I did:

y^4 - 15y^2 - 44 = 0

let y^2 = u

u^2 - 15u - 44 = 0

(u-11)(u-4) = 0

Therefore, u = 11 or u = 4

Sub that back into y^2 = u

y^2 = 11 or y^2 = 4

Therefore y = square root of 11 or y = square root of 4

$That factorisation is for $y^4 -15y^2\textbf{+ 44}$, rather than $-44$.$

please solve (1 Viewer)

brownie46

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sharoooooo

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InteGrand

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ashaaaa

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InteGrand

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