1) x^2-4=(х-2)(х+2)
2)25-9a^2=(5-3а)(5+3а)
3) 11m^2-11=11(m-1)(m+1)
4)6a^3-5xy^2= проверить правильность задания
5) 5x^3-5xy^2=5х(х^2-у^2)= 5х(х-у)(х+у)
6)a^4-b^6=(а^2) ^2- (b^3) ^2=( а^2- b^3)( а^2+ b^3)
7)
x^2-8xy+16y^2=(х-4у)^2
8)
a^2-14a+49=(а-7)^2
9) 3a-3b+ax-bx=3(а-b)+х(а-b)=(а-b)(3+х)
10)
7x^3-14x^5=7х^3(1-2х^2)
tg20°*tg40°*tg60°*tg80°=
=tg20°*(tg60-20°)*tg60°*tg(60°+20°)=
= [tg20°*tg(60°-20°)tg(60°+20°)]*tg60°=
=[tg20°*((sin60°-20°)*sin(60°+20°)/(cos(60°-20°)cos(60°+20°))]*√3 =
=[tg20°*(√3/2 *cos20° -1/2 * sin20°)(√3/2 *cos20° +1/2 * sin20°) :
(1/2*cos20°+√3/2 *sin20°)(1/2*cos20°-√3/2 *sin20°)]*√3 =
=[tg20°*(3/4*cos²20°-1/4sin²20°)/(1/4*cos20°-3/4sin20°)]*√3 =
=[(sin20°/cos20°)*(3cos²20°-sin²20°)/(cos²20°-3sin²20°)]*√3=
=[(3cos²20°*sin20°-sin³20°)/(cos³20°-3sin²20°cos20°)]*√3=
=(sin3*20°)/cos(3*20°)*√3= (sin60°)/(cos60°)*√3 = tg60°*√3 =√3*√3=3
X=260-y
0.03(260-y)+0.08y=13
7.8-0.03y+0.08y=13
0.05y=5.2
y=104
x=260-104
x=156