1)2x-5x²=0 2)5x²-20=0 3)7x+3+4x²=0 4)x²-9x+18=0 5)16k²+9-24k=0

1) x(2-5x)=0;
x=0. или 2-5x=0;
x=2/5.
2) 5x^2= 20;
x^2= 4;
x= плюс, минус 2
3) D= 49-4*4*3= 1.
x(1,2) = (-7+- 1)/2*4;
x(1)= -6/8= -3/4;
x(2)= -8/8= -1.
4) D= 81-4*18= 9.
x(1)= (9+3)/2= 6;
x(2)= (9-3)/2= 3.
5) D= 576-576=0
x=24/32=3/4.