20+х=45-4х
20+х-45+4х=0
5х-25=0
5х=25
х=5
1
3(a+5b)/[0,2(a-5b)(a+5b)]=15/(a-5b)
a-5b=0,4 15:0,4=37,5
2
7(a-2b)/[0,125(a-2b)(a+2b)]=56/(a+2b)
a+2b=14 56:14=4
3
[2x(x²-3)+3y(x²-3)]/[2y(x²6)]=(x²-3)(2x+3y)/[2y(x²-6)]
x/y=1/2⇒y=2x
(x²-3)*(2x+6x)/[4x(x²-6)]=2(x²-3)/(x²-6)
4
[3x(2y²+5)-y(2y²+5)]/[2x(2y²+5)]=(2y²+5)(3x-y)/[2x(2y²+5)]=(3x-y)/2x
x/y=1/7⇒y=7x (3x-7x)/2x=-4x/2x=-2
2х-2у=12 2х=12+2у х=6+у
4х+5у=24 4х+5у=24 4(6+у)+5у=24
4у+5у=24-24 х=6+0
9у=0 х=6
у=0
вроде так
10a^2-2ab+5ab-b^2-6a^2+3ab
1-28с+196с²=(1-14с)²=(1-14с)(1-14с)