Ответ:

Объяснение:

1)

a) (m+n)/(m-n)  -  (m-n)/(m+n)=

=(m+n)(m+n)-(m-n)(m-n)  / (m-n)(m+n)=

=(m+n)²-(m-n)² / (m²-n²) =

=(m+n+m-n)(m+n-m+n)  /(m²-n² =

= 2m*2n /(m²-n²)=

=4mn/(m²-n²)

b)

4y/(y²-x²)  -  2/(y-x)=   4y/(y-x)(y+x)   - 2/(y-x) =

=(4y-2(y+x) /(y-x)(y+x) =  (4y-2y-2x) /(y-x)(y+x)  =

=(2y-2x)/(y-x)(y+x) =2(y-x)/(y-x)(y+x)  = 2/(y+x)

c)

x²+7x+12=0

Δ=49-48=1

VΔ=1

x1=(-7+1)/2=-6/2=-3

x2=(-7-1)/2=-8/2=-4