k≠-4 k≠4
1/(k - 4) - 9/(k + 4) = 1/(k-4)*9/(k+4)
k + 4 - 9(k - 4) = 9
k + 4 - 9k + 36 = 9
-8k = -31
k = 31/8
У²-х²+ху²-ху² = (у-х)(х+у) + ху(у-х) = (у-х)(х+у+ху)
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(y^2-2y)^2 -y^2(y^2-9)+2y(2y^2+5)
y^4-4y-2y^2+9y^2+4y^2+7^y
y^4-2y^2+9y^2+4y+7y
y^4-11y^2+11y
y^4-11y