972. а) 5y(y^2-3)(y^2+3) = 5y(y^4-9) = 5y^5 - 45y
б) -8x(4x-x^3)(4x+x^3) = -8x(16x^2 - x^6) = -128x^3 + 8x^7
в) (a^4-3)(a^4+3)(a^8+9) = (a^8-9)(a^8+9) = a^16-81
г) (1-b^3)(1+b^3)(1+b^6) = (1-b^6)(1+b^6) = 1-b^12
973. а) (a+2)(a-2)-a(a-5) = a^2 - 4 - a^2 +5a = 5a - 4
б) (a-3)(3+a) + a(7-a) = a^2 - 9 + 7a - a^2 = 7a - 9
в) (b-4)(b+4)-(b-3)(b+5) = b^2 - 16 - (b^2 - 3b + 5b - 15) = b^2 - 16 - b^2 -2b + 15 = -2b - 1
г) (b+8)(b-6)-(b-7)(b+7) = b^2+8b-6b-48 - (b^2-49) = 2b - 48 + 49 =2b + 1
д) (c-1)(c+1)+(c-9)(c+9) = c^2 - 1 + c^2 - 81 = 2c^2 - 82
е) (5+c)(c-5) - (c-10)(c+10) = c^2 - 25 - (c^2 - 100) = c^2 - 25 - c^2 + 100 = -75
920. а) 4(m-n)^2 + 4m(m-n) = 4(m^2 - 2mn + n^2) + 4m^2 - 4mn = 4m^2 - 8mn + 4n^2 + 4m^2 - 4mn = 8m^2 + 4n^2 - 12mn
б) 5x(x-y) - 2(y-x)^2 = 5x^2 - 5xy - 2(y^2 -2xy+x^2) = 5x^2 - 5xy - 2y^2 + 4xy - 2x^2 = 3x^2-2y^2-xy
в) (y+7)^2 - 2(y+10)(y+4) = y^2+14y+49 - 2(y^2 + 10 y +4y + 40) = y^2+14y+49 - 2y^2-14y - 40 = -y^2 + 9
г) (x-5)(6+4x)-3(1-x)^2 = 6x - 30 + 4x^2 -20x -3(1-2x+x^2) = 4x^2 -14x -30 - 3 + 6x - 3x^2 = x^2 - 8x - 33