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The diagram below shows two right-angled triangles, ABC and ACD - Junior Cycle Mathematics - Question 8 - 2017

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Question 8

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The diagram below shows two right-angled triangles, ABC and ACD. They have right angles at B and D, respectively. $|AB| = 10$, $|AC| = 12$, and $|AD| = |DC| = x$, ... show full transcript

Worked Solution & Example Answer:The diagram below shows two right-angled triangles, ABC and ACD - Junior Cycle Mathematics - Question 8 - 2017

Step 1

Use trigonometry to find the size of the angle Y.

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Answer

To find angle YY, we can use the cosine ratio:

cosY=ABAC=1012\cos Y = \frac{|AB|}{|AC|} = \frac{10}{12}

Calculating:

Y=cos1(1012)Y = \cos^{-1}\left(\frac{10}{12}\right)

Using a calculator:

Y33.557Y \approx 33.557^{\circ}

Thus, the angle YY is approximately 33.6 degrees when rounded to one decimal place.

Step 2

Find the value of x.

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Answer

From triangle ABDABD, we can use the Pythagorean theorem:

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

Substituting the known values:

122=102+x212^2 = 10^2 + x^2

Which simplifies to:

144=100+x2144 = 100 + x^2

So:

x2=144100=44x^2 = 144 - 100 = 44

Therefore:

x=446.633x = \sqrt{44} \approx 6.633

Rounding to two decimal places, we find that x6.63x \approx 6.63.

Step 3

Find the size of the angle T.

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Answer

To find angle TT, we can use the properties of the circle.

Given:

PQR=22\angle PQR = 22^{\circ}

The relationship between angles subtended by the same arc states that:

PSR=PQR\angle PSR = \angle PQR

Therefore:

PSR=22\angle PSR = 22^{\circ}

Using the property that angles in the same segment are equal, we can express angle TT:

T=1802×PQR\angle T = 180^{\circ} - 2\times \angle PQR

Calculating:

T=1802×22=18044=136\angle T = 180^{\circ} - 2\times 22^{\circ} = 180^{\circ} - 44^{\circ} = 136^{\circ}

Thus, angle TT is 112 degrees.

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