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a in (-oo:+oo)
(4/5)*a-2/5 = -12/25 // + -12/25
(4/5)*a-2/5-(-12/25) = 0
(4/5)*a-2/5+12/25 = 0
4/5*a+2/25 = 0 // - 2/25
4/5*a = -2/25 // : 4/5
a = -2/25/4/5
a = -1/10
a = -1/10
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