1.(х-3у)(х+3у)=х²-9у²;
4а(а+6)-(а-8)²=4а²+24а-(а²-16а+64)=3а²+40а-64;
2. 5m+5n-k(m+n)=5(m+n)-k(m+n)=(m+n)(5-k);
t³-t²-81t+81=(t³-t²)-(81t-81)=
=t²(t-1)-81(t-1)=(t-1)(t²-81)=
=(t-1)(t-9)(t+9);
16p²-(7-p)²=
=16p²-(49-14p+p²)=15p²+
14p-49
3. y= -4x+3
x= -1/2
y= 2+3=5
y=23
-4x+3=23
-4x= 20
x= -5
4. ср.скор= (62+54)/2=58км/ч
5. скидка 1344*0,04=53,76руб
без 1344+53,76=1397,76руб
X = pi/6;
8(sin^2 x - cos^2 x) = - 8(cos^2 x - sin^2 x) = - 8*cos(2 x)=
= - 8 *cos(2*pi/6) = - 8* cos(pi/3) = - 8 * 1/2 = - 4
4х²+20х=0 12-48х₂=0 3х²-15=0 2х²+32=0 5х²-7х+2=0
х(4х+20)=0 -48х²=-12 3х²=15 2х²=-32 Д=49-4*5*2=9
4х+20=0 х²=-12/-48 х²=5 х²=-16 х₁=7-3/10=2/5
4х=-20 х²=0.25 х=+-√5 х=+-4 x₂=7+3/10=1
х=-5 х=+-0.5
{5a-3b=11
{3a + b = 1 ⇒ { b=1-3a
5a-3(1-3a) = 11
5a+9a-3=11
14a=14
a=1
b=1-3 = -2
Ответ: (1;-2)