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a in (-oo:+oo)
(5/7)*a-(1/4) = (-2/5)*a-(1907/140) // - (-2/5)*a-(1907/140)
(5/7)*a-((-2/5)*a)-(1/4)+1907/140 = 0
(5/7)*a+(2/5)*a-1/4+1907/140 = 0
39/35*a+468/35 = 0 // - 468/35
39/35*a = -468/35 // : 39/35
a = -468/35/39/35
a = -12
a = -12
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