result Not accurate

[guotie]

code:

func TestDecimalPow(t *testing.T) {
	d := decimal.NewFromInt(100)
	sqrt := d.Pow(decimal.NewFromFloat(0.5))
	t.Logf("sqrt: %v", sqrt) // 10

	d = decimal.NewFromBigInt(big.NewInt(100), 0)
	sqrt = d.Pow(decimal.NewFromFloat(0.5))
	t.Logf("sqrt: %v", sqrt) // 10

	d = decimal.NewFromBigInt(big.NewInt(10000), 0)
	d = d.Div(decimal.NewFromBigInt(big.NewInt(100), 0))
	sqrt = d.Pow(decimal.NewFromFloat(0.5))
	t.Logf("sqrt: %v", sqrt) // 9.99999999999999999999999999999999999999998
}

result:

sqrt: 10
sqrt: 10
sqrt: 9.99999999999999999999999999999999999999998

why?