Tg(a+b)=(tga+tgb)/1-tga*tgb)=(1/5+2/3)/(1-1/5*2/3)=1 ctg(a-b)= (1+3/2*5/2)/(3/2-5/2)=-4,75 tg(π/4+a)=(tgπ/4+tga)/(1-tgπ/4*tga)=(1+tga)/(1-tga) =(1+12/13*13/5)/(1-12/5) =17/7
C^2-0,49=c^2-49/100=(c-7/10)(c+7/10)
<em>cos 36° - cos 72° = 1/2</em>
<em>=> cos 36° - (2 cos^2(36°) - 1) = 1/2</em>
<em>=> cos 36° - 2 cos^2(36°) + 1 = 1/2</em>
<em>=> 4 cos^2(36°) - 2 cos 36° - 1 = 0</em>
[4y+3x=2/*2⇒8y+6x=4
{3y-7x=-x-15⇒3y-6x=-15
прибавим
11y=-11
y=-1
-4+3x=2
3x=6
x=2
Ответ (2;-1)
x²-3x-10≤0
x1+x2=3 U x1*x2=-10⇒x1=-2 U x2=5
x∈[-2;5]
![-14a^6b^5c^2/(-21a^2b^4c^5)=2a^4b/3c^3](https://tex.z-dn.net/?f=-14a%5E6b%5E5c%5E2%2F%28-21a%5E2b%5E4c%5E5%29%3D2a%5E4b%2F3c%5E3)
6x²+24x-72=0
6(x²+4x-12)=0
x1+x2=-4 U x1*x2=-12⇒x1=-6 U x2=2
4x²+20x-24=0
4(x²+5x-6)=0
x1+x2=-5 U x1*x2=-6⇒x1=-6 U x2=1
6(x+6)(x-2)/4(x+6)(x-1)=3(x-2)/2(x-1)