
Factorise the polynomials.

<h3><u>1. b² + 8b + 7</u></h3>

Factor the expression by grouping. First, the expression needs to be rewritten as b²+pb+qb+7. To find p and q, set up a system to be solved.

As pq is positive, p and q have the same sign. As p+q is positive, p and q are both positive. The only such pair is the system solution.

Rewrite
.

Take out the common factors.

Factor out common term b+1 by using distributive property.

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<h3><u>2. 4x² + 4x + 1</u></h3>

Factor the expression by grouping. First, the expression needs to be rewritten as 4x²+ax+bx+1. To find a and b, set up a system to be solved.

As ab is positive, a and b have the same sign. As a+b is positive, a and b are both positive. List all such integer pairs that give product 4.

Calculate the sum for each pair.

The solution is the pair that gives sum 4.

Rewrite
.

Factor out 2x in 4x² + 2x.

Factor out common term 2x+1 by using distributive property.

Rewrite as a binomial square.

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<h3><u>3. 5n² + 10n + 20</u></h3>

Factor out 5. Polynomial n² + 2n+4 is not factored as it does not have any rational roots.

<u>___________</u>_______
<h3><u>4. m³ - 729</u></h3>

Rewrite m³-729 as m³ - 9³. The difference of cubes can be factored using the rule:
. Polynomial m²+9m+81 is not factored as it does not have any rational roots.

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<h3><u>5. x² - 81</u></h3>

Rewrite x²-81 as x² - 9². The difference of squares can be factored using the rule:
.

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<h3><u>6. 15x² - 17x - 4</u></h3>

Factor the expression by grouping. First, the expression needs to be rewritten as 15x²+ax+bx-4. To find a and b, set up a system to be solved.

As ab is negative, a and b have the opposite signs. As a+b is negative, the negative number has greater absolute value than the positive. List all such integer pairs that give product -60.

Calculate the sum for each pair.

The solution is the pair that gives sum -17.

Rewrite
as
.

Factor out 5x in 15x²-20x.

Factor out common term 3x-4 by using distributive property.
