Bài 1:

a) \(25\left(x+2y\right)^2-16\left(2x-y\right)^2\)

\(=\left[5\left(x+2y\right)\right]^2-\left[4\left(2x-y\right)\right]^2\)

\(=\left[5\left(x+2y\right)-4\left(2x-y\right)\right]\left[5\left(x+2y\right)+4\left(2x-y\right)\right]\)

\(=\left(5x+10y-8x+4y\right)\left(5x+10y+8x-4y\right)\)

\(=\left(14y-3x\right)\left(13x+6y\right)\)

b) \(0,25\left(x-2y\right)^2-4\left(x+y\right)^2\)

\(=\left[\dfrac{1}{2}\left(x-2y\right)\right]^2-\left[2\left(x+y\right)\right]^2\)

\(=\left[\dfrac{1}{2}\left(x-2y\right)-2\left(x+y\right)\right]\left[\dfrac{1}{2}\left(x-2y\right)+2\left(x+y\right)\right]\)

\(=\left(\dfrac{1}{2}x-y-2x-2y\right)\left(\dfrac{1}{2}x-y+2x+2y\right)\)

\(=\left(-\dfrac{3}{2}x-3y\right)\left(\dfrac{5}{2}x+y\right)\)

\(=-3\left(\dfrac{1}{2}x+y\right)\left(\dfrac{5}{2}x+y\right)\)

c) \(\dfrac{4}{9}\left(x-3y\right)^2-0,04\left(x+y\right)^2\)

\(=\left[\dfrac{2}{3}\left(x-3y\right)\right]^2-\left[\dfrac{1}{5}\left(x+y\right)\right]^2\)

\(=\left[\dfrac{2}{3}\left(x-3y\right)-\dfrac{1}{5}\left(x+y\right)\right]\left[\dfrac{2}{3}\left(x-3y\right)+\dfrac{1}{5}\left(x+y\right)\right]\)

\(=\left(\dfrac{2}{3}x-2y-\dfrac{1}{5}x-\dfrac{1}{5}y\right)\left(\dfrac{2}{3}x-2y+\dfrac{1}{5}x+\dfrac{1}{5}y\right)\)

\(=\left(\dfrac{7}{15}x-\dfrac{11}{5}y\right)\left(\dfrac{13}{15}x-\dfrac{9}{5}y\right)\)

\(=\dfrac{1}{5}\left(\dfrac{7}{3}x-11y\right).\dfrac{1}{5}\left(\dfrac{13}{3}x-9y\right)\)

\(=\dfrac{1}{25}\left(\dfrac{7}{3}x-11y\right)\left(\dfrac{13}{3}x-9y\right)\)

d) \(-25x^2+30x-9\)

\(=-\left(25x^2-30x+9\right)\)

\(=-\left[\left(5x\right)^2-2.5x.3+3^2\right]\)

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

Bài 2:

a) \(x^3y^2-x^2y^3-2x+2y\)

\(=x^2y^2\left(x-y\right)-2\left(x-y\right)\)

\(=\left(x-y\right)\left(x^2y^2-2\right)\)

Thay x = -1 và y = -2 vào ta được

\(=\left[-1-\left(-2\right)\right]\left[\left(-1\right)^2\left(-2\right)^2-2\right]\)

\(=1\left(4-2\right)\)

\(=2\)

b) \(5x^2-3x+3y-5y^2\)

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

\(=5\left(x-y\right)\left(x+y\right)-3\left(x-y\right)\)

Thay x = 3 và y = 1 vào ta được

\(=5\left(3-1\right)\left(3+1\right)-3\left(3-1\right)\)

\(=5.2.4-3.2\)

\(=34\)

diện tích hình vuông là:

                                        18.75 : 3 = 6,25

 6,25 = 2,5 * 2,5 suy ra cạnh hình vuông là 2,5

a) \(\left(x^2+x\right)^2-2x^2-2x-15\)

\(=\left(x^2+x\right)^2-2\left(x^2+x\right)-15\)

Đặt x² + x = a

\(=a^2-2a-15\)

\(=a^2-2a+1-16\)

\(=\left(a-1\right)^2-16\)

\(=\left(a-1\right)^2-4^2\)

\(=\left(a-1-4\right)\left(a-1+4\right)\)

\(=\left(a-5\right)\left(a+3\right)\)

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

b) \(\left(x^2+2x\right)^2+9x^2+18x+20\)

\(=\left(x^2+2x\right)^2+9\left(x^2+2x\right)+20\)

Đặt x² + 2x = a

\(=a^2+9a+20\)

\(=a^2+4a+5a+20\)

\(=a\left(a+4\right)+5\left(a+4\right)\)

\(=\left(a+4\right)\left(a+5\right)\)

\(=\left(x^2+2x+4\right)\left(x^2+2x+5\right)\)

c) \(\left(x^2+3x+1\right)\left(x^2+3x+2\right)-6\)

Đặt x² + 3x + 1 = a

\(=a\left(a+1\right)-6\)

\(=a^2+a-6\)

\(=a^2-2a+3a-6\)

\(=a\left(a-2\right)+3\left(a-2\right)\)

\(=\left(a-2\right)\left(a+3\right)\)

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

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

d) \(\left(x+2\right)\left(x+3\right)\left(x+4\right)\left(x+5\right)-24\)

\(=\left[\left(x+2\right)\left(x+5\right)\right]\left[\left(x+3\right)\left(x+4\right)\right]-24\)

\(=\left(x^2+7x+10\right)\left(x^2+7x+12\right)-24\)

Đặt x² + 7x + 11 = a

\(=\left(a-1\right)\left(a+1\right)-24\)

\(=a^2-1-24\)

\(=a^2-25\)

\(=\left(a-5\right)\left(a+5\right)\)

\(=\left(x^2+7x+11-5\right)\left(x^2+7x+11+5\right)\)

\(=\left(x^2+7x-6\right)\left(x^2+7x+16\right)\)

là 3 chốc mk sẽ ghi lời giải cho bn

Lãi tháng đầu là :

   150000000 x 1.2% = 1800000 ( đồng )

Lãi tháng thứ hai là :

   (150000000+1800000) x 1.2% = 1821600 ( đồng )

Số tiền sau hai tháng người đó là :

   150000000 + (1821600 + 1800000) = 153621600 ( đồng )

          Đáp số : 153621600 đồng

the ki 11 chu sao nua the ma cung khong biet

con sâu phải đợi đến lúc thành bướm dồi bay

Coi giá bán là 100% thì tiền vốn là : 100%-20%=80%

tỉ số % lãi so với vốn là:20:80=0,25=25%

nhớ k cho mình nha

neu la n+1 tkì dễ hơn

40 tấn gạo