25*81= 5*5*9*9
корень равен 5*9=45
144*441=12*12*21*21
корень равен 12*21=252
4y=8, 4x-7y=-5; y=2, 4x-7*2=-5; y=2, 4x=9; y=2, x= 2.5
{2z + 5y = 63
{ z + 7y = 10 | * (-2)
{ 2z + 5y = 63
{ -2z -14y = - 20
(2z + 5y ) + ( - 2z - 14y) = 63 + ( - 20)
- 9y = 43
y = 43 : ( - 9) = - ⁴³/₉
у = - 4 ⁷/₉
z + 7 * (- 4 ⁷/₉) = 10
z + ⁷/₁ * ( - ⁴³/₉) = 10
z - ³⁰¹/₉ = 10
z - 33 ⁴/₉ = 10
z = 10 + 33 ⁴/₉
z = 43 ⁴/₉
Ответ : z = 43 ⁴/₉ ; у = - 4 ⁷/₉ .
(2m-3n)(5m+n)-10(m+n)² = 10m²+2mn-15mn-3n² -10(m²+2mn+n²) =
= 10m²+2mn-15mn-3n²-10m²-20mn-10n² = -33mn-13n² = -n(33m-13n)