Factorise the polynomials.
1. b² + 8b + 7
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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2. 4x² + 4x + 1
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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3. 5n² + 10n + 20
Factor out 5. Polynomial n² + 2n+4 is not factored as it does not have any rational roots.
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4. m³ - 729
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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5. x² - 81
Rewrite x²-81 as x² - 9². The difference of squares can be factored using the rule: .
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6. 15x² - 17x - 4
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.