Find the values of x + y if x^2 + y^2 = 36 and xy = -10.
I'm getting +4.226 and -4.226 but I don't think it's right. Anyone have any ideas?
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Find the values of x + y if x^2 + y^2 = 36 and xy = -10.
I'm getting +4.226 and -4.226 but I don't think it's right. Anyone have any ideas?
x^2 + y^2 = 36, xy = -10
x^2 = 100/y^2
100/y^2 + y^2 = 36
100 + y^4 = 36y^2
y^4 - 36y^2 + 100 = 0
y^2 = 18 +- 224^0.5
y = +- (18 +- 224^0.5)^0.5
x = +- (18 +- 224^0.5)^0.5
x=-5.741..
y=1.741..
x+y=-4
or
x=5.741..
y=-1.741..
x+y=4
ok:
x2 + y2 =36, xy = -10
=> x2 + 2xy + y2 = 16
look familiar?? of course, cos:
(x+y)2 = x2 + 2xy + y2
=> (x+y) = sqrt(16) = +/- 4!!
lol..
wow, I never thought of adding two eqn together like that.
x=+/- (sqr(9-2*sqr(14))*(4*sqr(7)+9*sqr(2)))/5
y=+/- sqr(-2(2*sqr(14)-9))