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The right-angled triangle ABC is shown in the diagram below - Junior Cycle Mathematics - Question 13 - 2016

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Question 13

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The right-angled triangle ABC is shown in the diagram below. The square BDEC is placed on the hypotenuse of this triangle. The area of the triangle ABC is 12a² squa... show full transcript

Worked Solution & Example Answer:The right-angled triangle ABC is shown in the diagram below - Junior Cycle Mathematics - Question 13 - 2016

Step 1

Step 1: Formula for the area of a triangle

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Answer

The area of a triangle is given by the formula:

Area=12×base×heightArea = \frac{1}{2} \times base \times height

In this case, we have:

12×(6a)×AC=12a2\frac{1}{2} \times (6a) \times |AC| = 12a²

Step 2

Step 2: Finding |AC|

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Answer

Rearranging the equation from Step 1 gives:

AC=12a2×26a=4a|AC| = \frac{12a² \times 2}{6a} = 4a

Thus, the length of side |AC| is 4a units.

Step 3

Step 3: Substitution into Pythagoras' Theorem

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Answer

Using the Pythagorean theorem:

AB2=AC2+BC2|AB|^2 = |AC|^2 + |BC|^2

Substituting the known values gives us:

(6a)2=(4a)2+BC2(6a)^2 = (4a)^2 + |BC|^2

Solving this yields:

36a2=16a2+BC236a^2 = 16a^2 + |BC|^2 BC2=36a216a2=20a2|BC|^2 = 36a^2 - 16a^2 = 20a^2

Thus, |BC| = √(20a²) = 2√5a.

Step 4

Step 4: Finding the area of BDEC

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Now, the area of the square BDEC can be found as follows:

Area=BC2=(25a)2=4imes5imesa2=20a2Area = |BC|^2 = (2√5a)^2 = 4 imes 5 imes a^2 = 20a^2

The area of square BDEC in terms of a² is thus 20a².

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