6. Упростите выражение: a) (m-0,5)(0,5+m); б) (4x+5y)(4x-5y); в) (6m-n²)(6m+n²).

a) $$(m-0.5)(0.5+m) = (m-0.5)(m+0.5) = m^2 - 0.5^2 = m^2 - 0.25$$. б) $$(4x+5y)(4x-5y) = (4x)^2 - (5y)^2 = 16x^2 - 25y^2$$. в) $$(6m-n^2)(6m+n^2) = (6m)^2 - (n^2)^2 = 36m^2 - n^4$$.