5x(2x +1) = 0 --> x = - 0.5
25 - 100x^2 = 25*(1 - 4x^2) = 25*(1 - 2x)(1+2x) --> x 1 = +0.5 x2 = - 0.5
25x^2 - 14 = 0; 25x^2 = 14 ; x^2 = 0.56 --> x = v 0.56
2x^2 - 8 = 0; 2x^2 = 8; x^2 = 4; x1= 2; x2 = -2
4x^2 - 12=0; 4x^2 = 12; x^2 = 3 ; x = v 3
x^2 - 10x = 0 ; x(x - 10) = 0--> x = 10
4x^2 + 20x = 0; 4x(x + 5)=0--> x = - 5
2x^2 + x = 0; x(x + 1) = 0 --> x = - 1
3x^2 - 27 = 0; 3(x^2 - 9)=0; 3(x-3)(x+3)=0--> x1 = 3; x2 = - 3
4x^2 + 20x = 0; 4x(x + 5) = 0; x = - 5
5x(2x +1) = 0 --> x = - 0.5
25 - 100x^2 = 25*(1 - 4x^2) = 25*(1 - 2x)(1+2x) --> x 1 = +0.5 x2 = - 0.5
25x^2 - 14 = 0; 25x^2 = 14 ; x^2 = 0.56 --> x = v 0.56
2x^2 - 8 = 0; 2x^2 = 8; x^2 = 4; x1= 2; x2 = -2
4x^2 - 12=0; 4x^2 = 12; x^2 = 3 ; x = v 3
x^2 - 10x = 0 ; x(x - 10) = 0--> x = 10
4x^2 + 20x = 0; 4x(x + 5)=0--> x = - 5
2x^2 + x = 0; x(x + 1) = 0 --> x = - 1
3x^2 - 27 = 0; 3(x^2 - 9)=0; 3(x-3)(x+3)=0--> x1 = 3; x2 = - 3
4x^2 + 20x = 0; 4x(x + 5) = 0; x = - 5
7^2x-6*7^x-7=0
7^x=t>0
t²-6t-7=0
t1=7 t2=-1<0
7^x=7⇒x=1
2) cos2x+sinx=0
1-2sin²x+sinx=0
2sin²x-sinx-1=0 решаем как квадратное через дискриминант
D=1-4*2*(-1)=9
sinx=(1-3)/4=-1/2 x=(-1)^(n+1)*π/6+πn, n∈Z
sinx=(1+3)/4=1 x=π/2+2πk, k∈Z
3)5sin²x+3sinxcosx+4cos²x=3
5sin²x+3sinxcosx+4cos²x-3(sin²x+cos²x)=0
5sin²x+3sinxcosx+4cos²x-3sin²x-3cos²x=0 однородное, разделим на cos²x
2sin²x+3sinxcosx+cos²x=0 | : cos²x
2tg²x+3tgx+1=0
D=9-4*2*1=1
tgx=(-3-1)/4=-1 x=-π/4+πn, n∈Z
tgx=(-3+1)/4=-1/2 x=-arctg1/2+πk, k∈Z