1) 5x^2 - 20 = 0
5x^2 = 20
x^2 = 4
x = 2
2) 0,64 - y^2 = 0
-y^2 = -0,64
y^2 = 0,64
y = 0,8
решил только а) <span> (5х+2)(х-1):5-(3х-5)(х+2):3=2</span>
<span>(3(5х+2)(х-1)-5(3х-5)(х+2))/15=2</span>
<span>3(5x^2-5x+2x-2)-5(3x^2+6x-5x-10=30</span>
<span>15x^2-15x+6x-6-15x^2-30x+25x-50=30</span>
<span>-14x=-14</span>
<span>x=1</span>
1) 21z+50=85
21z=85-50
21z=35
z=35/21=5/3
2) 19-2z=93
-2z=93+19
-2z=112
z=-56
3) 97-3z=72
-3z=72-97
-3z=-25
z=-25/-3
4) 21=69+6c
21-69=6c
48=6c
c=8
5) 97=4z+37
4z=37-97
4z=-60
z=-15
6) 87=35+13y
-13y=35-87
-13y=-52
y=4
7) 85=89+2z
-2z=89-85
-2z=4
z=-2
8) 14=7x-35
-7x=-35-14
-7x=-49
x=7