№1
(1-а)²= 1-2a+a²
(3+2у)²= 9+12y+4y²
(4х-5у)²= 16x²-40xy+25y²
№2
у²-49= y²-7² = (y-7)(y+7)
(5х-1)²-16х²= (5x-1)² - (4x)² = (5x-1-4x)(5x-1+4x) = (x-1)(9x-1)
9х²+30ху+25у²= (3х)²+2·3x·5y+(5у)²= (3x+5y)²
№3
(2-а²)(2+а²)= 2²-(a²)² = 4-a⁴
(e-3)(e+3)(e²+9)= (e²-3²)(e²+9) = (e²-9)(e²+9) = e⁴-81
№4
8,7²-1,3²= (8,7-1,3)·(8,7+1,3) = 7,4·10=74
107²-2+4·67+67²= не поняла условие
№5
(2x-1)(2x+1)-2(x-3)²=x(2x-3)
(2x)²-1²-2·(x²-6x+9)=2x²-3x
4x²-1 - 2x²+12x-18=2x²-3x
2x²+12x-19=2x²-3x
2x²+12x-19 - 2x²+3x = 0
15x=19
x=19:15
x=1 ⁴/₁₅
1/(n - 1) + (n - 2)/(n² - n) = 1/(n - 1) + (n - 2)/(n(n - 1)) =
= (n + (n - 2))/(n(n - 1)) = (2n - 2)/(n(n - 1)) = 2(n - 1)/n(n - 1)) =
= 2/n