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Mathematics 21 Online
OpenStudy (nosnip):

How to I factorise/solve this equation?

OpenStudy (nosnip):

\[y ^{2} - x - 6x ^{2}\]

OpenStudy (nosnip):

= 0

OpenStudy (nosnip):

Do you know what type of equation it even is so I can google it?

OpenStudy (unklerhaukus):

you can rearrange it \[y^2−x−6x^2 = 0\] \[0 = 6x^2+x-y^2\] so it looks like a quadratic, where \(a= 6\), \(b=1\), \(c=-y^2\) solve with the quadratic formula

OpenStudy (nosnip):

ah okay that's I wasn't sure if it was a quadratic :)

OpenStudy (unklerhaukus):

(i'm assuming there is no other information give about y)

OpenStudy (nosnip):

well it's part of a simultaneous equation? I'm confused because it's a non-calculator question and this seems difficult without a calculator

OpenStudy (nosnip):

\[y - 3x + 2 = 0\] \[y ^{2} - x - 6x ^{2} = 0\]

OpenStudy (unklerhaukus):

so you have two equations?

OpenStudy (unklerhaukus):

What do you get if you solve the first one \[y-3x+2=0\]for \(y\)?

OpenStudy (nosnip):

y = 3x + 2

OpenStudy (unklerhaukus):

substitute this into the second equation \[y^2−x−6x^2=0\\ \downarrow\\ (3x + 2)^2-x-6x^2 =0\] This is a quadratic equation in \(x\), solve for both values of \(x\)

OpenStudy (unklerhaukus):

(after simplifying)

OpenStudy (nosnip):

okay give me a second :)

OpenStudy (nosnip):

Do you get the quadratic \[3x ^{2} + 11x + 4 = 0\]

OpenStudy (unklerhaukus):

almost, but the middle term isn't right

OpenStudy (nosnip):

I'm not sure what else it could be?

OpenStudy (unklerhaukus):

What did you get for the expansion of \[(3x-2)^2=\]

OpenStudy (nosnip):

\[9x ^{2} + 12x +4\]

OpenStudy (unklerhaukus):

\[(a-b)^2=a^2-2ab+b^2\]

OpenStudy (nosnip):

I'm still not seeing where I went wrong sorry!

OpenStudy (unklerhaukus):

the +12 should be -12

OpenStudy (nosnip):

ooh yes sorry you're right okay I can do it myself from there thankyou :)

OpenStudy (nosnip):

I've got to go out but thatnlyou for your help I will give it a go later

OpenStudy (unklerhaukus):

you should now use the quadratic formula on the right (simplified) quadratic equation to get two nice values of x, then back substitute into equation 1, to get the corresponding y's

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