Evaluate the following products without multiplying directly
$103 \times 105$
Expand
$(2 a+3 b)(2 a-5 b)$
Expand
$(x+5 y)(x-5 y)$
Expand
$\left(x-\frac{1}{2}\right)^{2}$
Factorise the following quadratic polynomials by splitting the middle term
$x^{2}+10 x+16$