а) 1,2x^2-7,5x=0
x(1.2x-7.5)=0
x=0 или 1.2x-7.5=0
1.2x=7.5
x=6,25
---------------------------------------------------------------------------
б) х^2-13=0
x^2=13
x= + - корень из 13
-----------------------------------------------
в) 4y^2-25=75
4y^2=75+25
4y^2=100
y^2=100/4
y^2=25
y = -5 и y=+5
=======================================================