See, in this we should be very careful in multiplying two polynomials.And keep in mind that Each and every term of each polynomial will multiply with the each term of another polynomial. I hope this will help u!
A=3x²-2x-5 , B=-4x²-5x-1
A × B ⇒ ( 3x² - 2x - 5 ) ( - 4x² - 5x - 1 )
⇒ - 12x⁴ - 15x³ - 3x² + 8x³ + 10x² + 2x + 20x² + 25x + 5
A × B⇒ - 12x⁴ - 7x³ + 27x² + 27 x + 5 Ans.