121.
1) (b+6)(b-6)-3b(b+2) = b²-36-3b²-6b = -2b²-36-6b = -2b²-6b-36
2) (3a-2)(3a+2)+(a-8)(a+8) = 9a²-4+a²-64 = 10a²-68
3) (5x-3y)(5x+3y)+(3x-5y)(3x+5y) = 25x²-9y²+9x²-25y² = 34x²-34y²
4) (c-2)(3-c)-(5-c)(5+c) = 3c-c²+6+2c-(25-c²) = 3c-c²-6+2c-25+c² = 5c-31
5) (x-5)²-x(x+3) = x²-10x+25-x²-3x = -13x+25
6) (6a-b)²-(9a-b)(4a+2b) = 36a²-12ab+b²-(36a²+18ab-4ab-2b²) = 36a²-12ab+b²-(36a²+14ab-2b²) = 36a²-12ab+b²-36a²-14ab+2b² = -26ab+3b²
7) 3x(5+x)²-x(3x-6)² = 3x(25+10x+x²)-x(9x²-36x+36) = 75x+30x²+3x³-9x³+36x²-36x = 39x+66x²-6x³ = -6x³+66x²+39x
8) (x-2)²+(x-1)(x+1) = x²-4x+4+x²-1 = 2x²-4x+3
9) (3a-2b)(3a+2b)-(a+3b)² = 9a²-4b²-(a²+6ab+9b²) = 9a²-4b²-a²-6ab-9b² = 8a²-13b²-6ab
123.
1) x²-25 = (x-5)(x+5)
2) 36-16y² = 4(3-2y)(3+2y)
3) 4x²-81y² = (2x-9y)(2x+9y)
4) 0,09t²-121p² = (0,3t-11p)(0,3t+11p)
5) 100a²-180ab+81b² = (10a-9b)²
6) 16m²+49n²-56mn = 16m²-56mn+49n² = (4m-7n)²
129.
(x-3)²-(x+1)² = 12
x²-6x+9-(x²+2x+1) = 12
x²-6x+9-x²-2x-1 = 12
-8x+8 = 12
-8x = 12-8
-8x = 4
x = - 4/8
x = - 1/2
Ответ: - 1/2
135.
(x+7)²+2(x+7)(x-5)+(x-5)² = x²+14x+49+(2x+14)(x-5)+x²-10x+25 = x²+14x+49+2x²-10x+14x-70+x²-10x+25 = 4x²+8x+4
4x²+8x+4 = 4×3²+8×3+4 = 4×9+24+4 = 36+24+4 = 64