60 + 20 x 2 + 900

= 60 + 40 + 900

= 100 + 900

= 1000

_Ai k mk thì mk k lại_

60+20x2+900

=60+40+900

=100+900

=1000

ai k mình mình k lại

\(A=x^4+4x^3+10x^2+12x=x^4+4x^2+9+4x^3+12x+6x^2-9\)

<=>\(A=x^4+4x^2+9+4x^3+12x+6x^2-9\)

<=>\(A=\left(x^2\right)^2+\left(2x\right)^2+3^2+2.x^2.2x+2.2x.3+2.x^2.3-9\)

<=>\(A=\left(x^2+2x+3\right)^2-9\)

<=>\(A=\left[\left(x+1\right)^2+2\right]^2-9\)

Vì \(\left(x+1\right)^2\ge0\Leftrightarrow\left(x+1\right)^2+2\ge2\Leftrightarrow\left[\left(x+1\right)^2+2\right]^2\ge4\)\(\Leftrightarrow A=\left[\left(x+1\right)^2+2\right]^2-9\ge-5\)

=>A_min=-5 <=> x=-1

Vậy A_min=5 tại x=-1

\(\frac{x}{3}=\frac{y}{4}\)

\(\Rightarrow4x=3y\)

\(\Rightarrow\frac{x}{y}=\frac{3}{4}\)

\(\Rightarrow\orbr{\begin{cases}x=3\\x=-3\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}y=4\\y=-4\end{cases}}\)

5x²-5x-6=(x+1)(5x-6)

ok k hộ mình cái

1² - 2² + 3² - 4² + 5² - 6² + ... + 2009² - 2010² + 2011²

= (1 - 2).(1 + 2) + (3 - 4).(3 + 4) + (5 - 6).(5 + 6) + ... + (2009 - 2010).(2009 + 2010) + 2011²

= -3 + (-7) + (-11) + ... + (-4019) + 2011²

= -(1 + 2 + 3 + 4 + 5 + 6 + ... + 2009 + 2010) + 2011²

\(=-\frac{\left(1+2010\right).2010}{2}+2011^2\)

\(=-2011.1005+2011^2\)

= 2011.(2011 - 1005)

= 2011.1006

= 2023066

câu 8 

x+y+z=2

câu9

12

câu 10

4

ok

c8

2

c9

12

c10

4

Ta có : (a + b + c)² = a² + b² + c² + ab + bc + ca

13² = 85 + ab + bc + ca

ab + bc + ca = 169 - 85 = 84

(a+b+c)² = a² + b² + c² + 2(ab +bc +ac)

ab+bc+ac = 84/2 =42

90 + 90 + 90 + 30 = 300

k mk nhé

90 + 90 + 90 + 30 = 300

nha bn k mk nha bn

aj k mk mk sẽ k laj