x²+21x+80
a)x1+x2=-21, x1x2=80, x1=-5,x2=-16
x²+21x+80=(x+5)(x+16)
b)D=b²-4ac, b=21, a=1, c=80
D=441-320=121, √D=√121=11
x1=(-21+11)/2=-5 , x2=(-21-11)/2=-32/2=-16
1.(7-3х)^2=49-42х+9х^2
2.(6m-n)(6m+n)=36m^2-n^2
3.42ab-(3a+7b)^2=42ab-9a^2-42ab-49b^2=-9a^2-49b^2
4.(m-5n)(m+5n)(5n-1)^2=m^2-25n^2+25n^2+10n+1=m^2+10n+1
5.49m^2+N+36n^2 по формуле (a+b)^2=a^2+2ab+b^2; N=84mn
x-y=2
составим сооьношение
1,6м-8м
5м-х
8*5/1,6=25