1.49-(4х^2+12x+9)=0

49-4x^2-12x-9=0

-4x^2-12x+40=0 |*(-1)

4x^2+12x-40=0|:4

x^2+3x-10=0

D=9+40=49

x1=-3+7/2=2

х2=-3-7/2=-5

2. x^2+2x+1-(9x^2-6x+1)=0

x^2+2x+1-9x^2+6x-1=0

-8x^2+8x=0/:8

-x^2+x=0/*-1

x^2-x=0

x(x-1)=0

x1=0   x2=1

3. 81--(25-70x+49x^2)=0

81-25+70x-49x^2=0

56+70x-49x^2=0/:7

8+10x-7x^2=0/*-1

7x^2-10x-8=0

D=100+224=324

x1=10+18/14=2

x2=10-18/14=-4/7