Solve the simultaneous equations: x^2+y^2=36 ; x=2y+6

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Substitute x in terms of y into the first equation:

(2y+6)2+y2=36

Use FOIL to expand the brackets

4y2+24y+36+y2=36  =>   5y2+24y=0

y(5y+24)=0  =>  y=0   or    y=(-24)/5

Substitute these values of y into the second equation to find x

when y=0, x=2*0+6  =>  x=6

when y=(-24)/5,  x=2*(-24)/5+6  =>  x=-3.6

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