Answer 1

 Here, we will use the identity​ \[\left( x - a \right)\left( x + b \right) = x^2 + \left( b - a \right)x - ab\].

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

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

\[ = 4 x^4 + 4 x^2 - 15\]