\(\left(x-3\right)\left(x-5\right)-\left(x-4\right)^2\)
\(=x^2-5x-3x+15-\left(x^2-8x+16\right)\)
\(=x^2-5x-3x+15-x^2+8x-16\)
\(=x^2-x^2-8x+8x+15-16=-1\)
(x - 3)(x - 5) - (x - 4)²
= x² - 5x - 3x + 15 - x² + 8x - 16
= (x² - x²) + (-5x - 3x + 8x) + (15 - 16)
= -1
\(\left(x-3\right).\left(x-5\right)-\left(x-4\right)^2\)
\(=x-3.x-5=x^2-5x-3x+15\)
\(=x^2-8x+15\)
\(=\left(x-4\right)^2=\left(x-4\right).\left(x-4\right)\)
\(=x^2-4x-4x+16=x^2-8x+16\)
\(=\left(x^2-8x+15\right)-\left(x^2-8x+16\right)\)
\(=x^2+8x-16=-1\)
Vậy giá trị cần tìm là: \(-1\)