X^2/16+y^2/4=1 надо выразить у(игрик)
x^2/16+y^2/4=1|*16
x^2+4y^2=16
4y^2=16-x^2
y^2=(16-x^2):4
y=+-sqr((16-x^2):4)
y=+-sqr(16-x^2):2
y=+-sqr((4-x)(4+x)):2
1)y^2/4=1-x^2/16 2)y^2=(1-x^2/16)*4 3)y1=sqrt((1-x^2/16)*4) 4)y2=-sqrt((1-x^2/16)*4)