<span>(2y-1)^2 -4(y-2)(y+2)=-5y+18
4y²-4y+1-4y²+16=-5y+18
y-1=0
y=1
</span>
5а = 35 - 6б
а = 7 - 1,2 б
просто переносишь и сокращаешь
1/2cos2x+1/2cos4x-cos2x=0
1/2cos4x-1/2cos2x=0
1/2*(2cos²2x-1)-1/2cos2x=0
cos²2x-1/2cos2x-1/2=0
cos2x=a
a²-0,5a-0,5a=0
D=0,25+2=2,25
a1=(0,5-1,5)/2=-0,5⇒cos2x=-0,5⇒2x=+-5π/6+2πn⇒x=+-5π/12+πn
a2=(0,5+1,5)/2=1⇒cos2x=1⇒2x=2πn⇒x=πn
Вот...................................
1-1.24n+1.44n^2=(1-1.2n)^2
4x^2+5.2xy+1.69y^2=(2x+1.3y)^2
<span>81a^2+23,4a+1,69=(9a+1.3)^2
</span><span>36a^2−22,8a+3,61=(6a+1.9)^2
</span><span>49−182n+169n^2=(7-13n)^2</span>