Ответ:
1) 4х² - 20 = 0
4(х²-5)= 0
х²=5
х = ±√5
2) 3х²+5х=0
х(3х+5)=0
3х+5=0
3х= -5
х= -5/3
3) х²-5х-24=0
а = 1; b= -5; c= -24
D = b²-4ac = (-5)²-4*1*(-24) = 25 + 96 = 121
x1 = (5+11)/2= 16/2 = 8
x2 = (5-11)/2 = -6/2 = -3
4)7x²-22x+3= 0
a = 7; b = -22; c = 3
D = 484- 4*7*3 = 484 -84= 400
x1 = (22+20)/14 = 42/14 = 3
x2= (22-20)/14 = 2/14 = 1/7
5)7x²-6x+2=0
D= 36-4*7*2 = 36-56= -20, коренів немає
6) 4x²+12x+9= 0
a=4 b= 12 c= 9
D= 144-4*4*9 = 144-144= 0
x = -12/8 = -1.5
номер 2
x1+x2 = 6
x1*x2 = 4
x²-6x+4=0