Question:
Tick (✓) the correct answer:
(2x + 5)(2x − 5) = ?
(a) (4x2 + 25)
(b) (4x2 − 25)
(c) (4x2 − 10x + 25)
(d) (4x2 + 10x − 25)
Solution:
(b) $\left(4 x^{2}-25\right)$
$(2 x+5)(2 x-5)$
$\Rightarrow(2 x)^{2}-(5)^{2}$ (according to the formula $\left.(a+b)(a-b)=a^{2}-b^{2}\right)$
$\Rightarrow 4 x^{2}-25$