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a in (-oo:+oo)
(-4/7)*a = 8/7 // - 8/7
(-4/7)*a-(8/7) = 0
(-4/7)*a-8/7 = 0
-4/7*a-8/7 = 0 // + 8/7
-4/7*a = 8/7 // : -4/7
a = 8/7/(-4/7)
a = -2
a = -2
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