a\(\left(x-3\right)^2-\left(x+2\right)^2-5\left(\frac{1}{5}-7\right)=-30\)

=>(x-3-x-2)(x-3+x+2)-x+35=-30

=>-5(2x-1)-x+35=-30

=>-10x+5-x+35=-30

=>-11x+40=-30

=>-11x=-70 =>x=70/11

d)\(\left(x+3\right)^2-\left(x+5\right)\left(x-5\right)=2\)

\(=>\left(x+3\right)^2-x^2+25=2\)

\(=>\left(z+3-z\right)\left(z+3+z\right)+25=2\)

\(=>3\left(2z+3\right)+25-2=0\)

\(=>6z+9+23=0\)

\(=>6x+32=0=>6x=-32=>x=-\frac{16}{3}\)

e)\(3\left(x+2\right)^2+\left(2x-1\right)^2-7\left(x+3\right)\left(x-3\right)=36\)

\(=>3\left(x^2+4x+4\right)+\left(4x^2-4x+1\right)-7\left(x^2-9\right)=36\)

\(=>3x^2+12x+12+4x^2-4x+1-7x^2+63\)

\(=>8x+76=36=>8x=36-76=>x=-40\div8=-5\)

g)\(\left(x-1\right)\left(x^2+x+1\right)-x\left(x+2\right)\left(x-2\right)=5\)

\(=>x^3-1-x\left(x^2-4\right)=5=>x^3-1-x^3+4x=5\)

\(=>4x-1=5=>4x=6=>x=\frac{3}{2}\)

Bạn vào câu hỏi tương tự nha !!! Tích mình nhé !

• thutrangdoan289
• 18/12/2019

Bài 5:

a) Chứng minh (2n+5)2−25(2n+5)2−25 chia hết cho 44 với mọi n∈Z.n∈Z.

Ta có: (2n+5)2−25=4n2+20n+25−25=4n2+20n=4n(n+5).(2n+5)2−25=4n2+20n+25−25=4n2+20n=4n(n+5).

Vì 4⋮4⇒4n(n+5)⋮4∀n∈Z.

# Chúc bạn học tốt!

a) x^2+3x=0
<=> x(x+3)=0
<=> x+3=0 

---> X=-3
b)x.(x-7).(x+7)=0 

<=>x.(x^2-7^2)=0
<=> X^2-7^2=0
==>x= 7 và x=-7
c) x^3-9x=0
<=> x(x^2-3^2)=0
<=> x^2-3^2=0
~~> x = 3 và x=-3
d) x^2-5x-6=0
<=> x^2-5x-5-1=0
<=> (x^2-1)-(5x-5) =0
<=> x(x-1) - 5(x-1)=0
<=> (x-1)(x-5)=0
~~> x-1 = 0 ~> x=1
~~> x-5=0 ~~> x=5
Vậy x=1 và x=5