\(\left(x^2+4x+3\right)\left(x^2+12x+35\right)+15\)
\(=\left(x^2+2.x.2+2^2-1\right)\left(x^2+2.x.6+6^2-1\right)+15\)
\(=\left[\left(x+2\right)^2-1\right]\left[\left(x+6\right)^2-1\right]+15\)
\(=\left[\left(x+2\right)^2-1^2\right]\left[\left(x+6\right)^2-1^2\right]+15\)
\(=\left(x+2-1\right)\left(x+2+1\right)\left(x+6-1\right)\left(x+6+1\right)+15\)
\(=\left(x+1\right)\left(x+3\right)\left(x+5\right)\left(x+7\right)+15\)
\(=\left[\left(x+1\right)\left(x+7\right)\right]\left[\left(x+3\right)\left(x+5\right)\right]+15\)
\(=\left(x^2+7x+x+7\right)\left(x^2+5x+3x+15\right)+15\)
\(=\left(x^2+8x+7\right)\left(x^2+8x+15\right)+15\)
mk chỉ lm đc đến đây thôi nha bn @♂ Batman ♂
