माख: (i) 15 - 2x - x2 and (iii) x2 + 8x - 20

Step 1: Identify the expression to be factored. The expression is $x^2 + 8x - 20$.

Step 2: Find two numbers that multiply to the constant term $(-20)$ and add up to the coefficient of the middle term $(8)$. Let these two numbers be $p$ and $q$. We need $p \times q = -20$ and $p + q = 8$. Consider the factors of -20:

• $1 \times -20 = -20$, $1 + (-20) = -19$
• $-1 \times 20 = -20$, $-1 + 20 = 19$
• $2 \times -10 = -20$, $2 + (-10) = -8$
• $-2 \times 10 = -20$, $-2 + 10 = 8$ The numbers are $-2$ and $10$.

Step 3: Rewrite the middle term using these two numbers. $x^2 + 8x - 20 = x^2 - 2x + 10x - 20$

Step 4: Factor by grouping. Group the first two terms and the last two terms: $(x^2 - 2x) + (10x - 20)$ Factor out the common factor from each group: $x(x - 2) + 10(x - 2)$

Step 5: Factor out the common binomial factor $(x - 2)$. $(x - 2)(x + 10)$

The factored form of the expression is $\boxed{(x-2)(x+10)}$.