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.