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Help with a simultaneous equation PLEASE

Hi- I have been struggling with this BBC bitesize grade 8 simultaneous equation!
I know the answers are
x=-4 y=1/2 or x= 5/2 y=-11/4

I really need to understand the steps to get me there as I can’t work out what to do with the
-2xy

This is the question!

Solve the simultaneous equations:
x+2y=-3 x^2-2xy=20

Thank you to anyone who can help!🙏
Reply 1
Original post by Lis Walker
Hi- I have been struggling with this BBC bitesize grade 8 simultaneous equation!
I know the answers are
x=-4 y=1/2 or x= 5/2 y=-11/4

I really need to understand the steps to get me there as I can’t work out what to do with the
-2xy

This is the question!

Solve the simultaneous equations:
x+2y=-3 x^2-2xy=20

Thank you to anyone who can help!🙏

Just solve using substitution, so rearrange the first to give
y = ...
then sub into the second and solve the quadratic in x.
Reply 2
Original post by mqb2766
Just solve using substitution, so rearrange the first to give
y = ...
then sub into the second and solve the quadratic in x.

Thanks! That’s what I’m struggling with!😂
Was hoping for a step by step solution that I could follow!🙄
Reply 3
Original post by Lis Walker
Thanks! That’s what I’m struggling with!😂
Was hoping for a step by step solution that I could follow!🙄

Which part are you struggling with? It would help to post what youd tried, even if its not correct.
Reply 4
I’ve had so many attempts! I’m ok with x+2y=-3 but I don’t know how to substitute that into the other equation when it domes to -2xy and then how to get from that to two values for x and y!

I never said I was good at maths!😵*💫
Reply 5
Original post by Lis Walker
I’ve had so many attempts! I’m ok with x+2y=-3 but I don’t know how to substitute that into the other equation when it domes to -2xy and then how to get from that to two values for x and y!

I never said I was good at maths!😵*💫

Rearrange the first equation in terms of y so
y = ...
so just like an equation of a line, then replace the y (substitute) in the second equation with the equivalent expression in terrms of x. You should be able to rearrange the first equation and try substituting, so upload what youve tried.
(edited 2 months ago)
Reply 6
Original post by mqb2766
Rearrange the first equation in terms of y so
y = ...
so just like an equation of a line, then replace the y (substitute) in the second equation with the equivalent expression in terrms of x. You should be able to rearrange the first equation and try substituting, so upload what youve tried.

Thanks so much!

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