6х^2 +21x-2x-7-6x^2+5x-6x+5=7
21x-2x+5x-06x=7+7-5
18x=9
x=9/18
x=1/2;0,5
(х²-25)²+(х²+3х-10)²=0
(x-5)²·(x+5)²+(x-2)²(x+5)²=0
(x+5)²·((x-5)²+(x-2)²0=0
(x+5)²·(x²-10x+25+x²-4x+4)=0
(x+5)²·(2x²-14x+29)=0
x+5=0 или 2x²-14x+29=0
x=-5 D=196-4·2·29<0
нет корней
Ответ. х=-5
1) a³-5a²+7a-11=(a³-5a²)+(7a-11)
2) a³-5a²+7a-11=a³-(5a²-7a+11)
(10x+3y)^2-(8x+4y)(8x-4y)=100x^2+60xy+9y^2-64x^2-16y^2=36x^2+6xy-7y^2