用公式法解方程:5x2-4x-1=0
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5x^2 - 4x -1 = 0
==> x = {-(-4) ±√[(-4)^2 - 4 * 5 * (-1)]} / (2 * 5)
==> x = { 4 ±√[16 + 20]} / (2 * 5)
==> x = { 4 ±√[36]} / (10)
==> x = { 4 ± 6} / (10)
==> x = 10/10 or x = -2/10
==> x =1 or x = -1/5
==> x = {-(-4) ±√[(-4)^2 - 4 * 5 * (-1)]} / (2 * 5)
==> x = { 4 ±√[16 + 20]} / (2 * 5)
==> x = { 4 ±√[36]} / (10)
==> x = { 4 ± 6} / (10)
==> x = 10/10 or x = -2/10
==> x =1 or x = -1/5
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