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The diagram shows a right-angled triangular prism ABCDEF - OCR - GCSE Maths - Question 18 - 2019 - Paper 4

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The diagram shows a right-angled triangular prism ABCDEF. Length AD = 11 cm, length CD = 10 cm and length CF = 6 cm. (a) Calculate the volume of the prism. (b) Us... show full transcript

Worked Solution & Example Answer:The diagram shows a right-angled triangular prism ABCDEF - OCR - GCSE Maths - Question 18 - 2019 - Paper 4

Step 1

(a) Calculate the volume of the prism.

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Answer

To calculate the volume of the prism, we use the formula:

V=extBaseAreaimesextHeightV = ext{Base Area} imes ext{Height}

The base is a right triangle with legs CD and CF. So, the area of the base is:

extBaseArea=12×CD×CF=12×10×6=30cm2 ext{Base Area} = \frac{1}{2} \times CD \times CF = \frac{1}{2} \times 10 \times 6 = 30 \, \text{cm}^2

The height of the prism is the length AD, which is 11 cm.

Now we can calculate the volume:

V=30cm2×11cm=330cm3V = 30 \, \text{cm}^2 \times 11 \, \text{cm} = 330 \, \text{cm}^3

Step 2

(b) Use trigonometry to show that angle FDC = 31°, correct to the nearest degree.

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Answer

To find angle FDC, we can use the tangent function:

tan(FDC)=CDCF=106\tan(FDC) = \frac{CD}{CF} = \frac{10}{6}

Calculating this gives:

FDC=tan1(106)30.96°FDC = \tan^{-1}\left(\frac{10}{6}\right) \approx 30.96°

Rounding to the nearest degree, we find:

FDC31°FDC \approx 31°

Step 3

(c) Calculate the exact length of AF.

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Answer

To find the length of AF, we can use the Pythagorean theorem in triangle ACD:

Let AC be the length we need to find. Then:

AC2=AD2+CD2AC^2 = AD^2 + CD^2

Substituting the known values:

AC2=112+102=121+100=221AC^2 = 11^2 + 10^2 = 121 + 100 = 221

So,

AC=221AC = \sqrt{221}

Thus, the length of AF is:

AF=AC+CF=221+6AF = AC + CF = \sqrt{221} + 6

Calculating this gives:

AF=14.8cmext(approximately)AF = 14.8 \, \text{cm} ext{ (approximately)}

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