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Factorise $n^{2} - 11n + 18$ - Junior Cycle Mathematics - Question 12 - 2017

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Factorise $n^{2} - 11n + 18$. Factorise fully $wy - y - 1 + w$. Find the value of $ rac{5}{3x^{2}} - rac{7}{6x-12}$ when $x = 4$. Use factorisation to simplify $... show full transcript

Worked Solution & Example Answer:Factorise $n^{2} - 11n + 18$ - Junior Cycle Mathematics - Question 12 - 2017

Step 1

Factorise $n^{2} - 11n + 18$

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Answer

To factorise the quadratic expression, we seek two numbers that multiply to 1818 and add to 11-11. The numbers 2-2 and 9-9 satisfy this condition. Therefore, we can write:

n211n+18=(n2)(n9)n^{2} - 11n + 18 = (n - 2)(n - 9)

Step 2

Factorise fully $wy - y - 1 + w$

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Answer

First, we can rearrange the terms:

wy+wy1wy + w - y - 1

Now, we can factor by grouping:

w(y+1)1(y+1)=(w1)(y+1)w(y + 1) - 1(y + 1) = (w - 1)(y + 1)

Step 3

Find the value of $\frac{5}{3x^{2}} - \frac{7}{6x - 12}$ when $x = 4$

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Answer

First, substitute x=4x = 4 into the expression:

53(4)276(4)12=548724\frac{5}{3(4)^{2}} - \frac{7}{6(4) - 12} = \frac{5}{48} - \frac{7}{24}

Next, convert 724\frac{7}{24} to have a common denominator of 4848:

724=1448\frac{7}{24} = \frac{14}{48}

So, the expression becomes:

5481448=948=316\frac{5}{48} - \frac{14}{48} = \frac{-9}{48} = -\frac{3}{16}

Step 4

Use factorisation to simplify $4e^{2} - 9$

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Answer

Recognizing that 4e294e^{2} - 9 is a difference of squares, we can factor it as:

4e29=(2e)232=(2e3)(2e+3)4e^{2} - 9 = (2e)^{2} - 3^{2} = (2e - 3)(2e + 3)

Step 5

Find the value of $a$, the value of $b$, and the value of $c$

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Answer

We are given that the area of the rectangle can be represented as:

2x313x2+25x122x^{3} - 13x^{2} + 25x - 12

Substituting x3x - 3 into the expression:

x3=0x=3x - 3 = 0 \Rightarrow x = 3

Therefore, the factors are:

x2(ax2+bx+c)=2x313x2+25x12x^{2}(ax^{2} + bx + c) = 2x^{3} - 13x^{2} + 25x - 12

By polynomial long division, the coefficients yield:

  • a=2a = 2
  • b=7b = -7
  • c=4c = 4

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