Math Problem Statement

The diagram shows parallelogram EFGH. (a) Work out the area of the parallelogram. Give your answer correct to 3 significant figures. (b) Work out the length of the diagonal EG of the parallelogram. Give your answer correct to 3 significant figures.

Solution

Let's solve the problem based on the uploaded image.

(a) Work out the area of the parallelogram:

The formula for the area of a parallelogram is:
Area=Base×Height\text{Area} = \text{Base} \times \text{Height}
Alternatively, when the angle between two sides is given:
Area=a×b×sin(θ)\text{Area} = a \times b \times \sin(\theta)
where:

  • a=9.3cma = 9.3 \, \text{cm} (side EFEF),
  • b=14.7cmb = 14.7 \, \text{cm} (side FGFG),
  • θ=106\theta = 106^\circ (angle EFGEFG).

First, calculate sin(106)\sin(106^\circ):
sin(106)0.961\sin(106^\circ) \approx 0.961.

Now substitute into the formula:
Area=9.3×14.7×0.961\text{Area} = 9.3 \times 14.7 \times 0.961
Area131.2cm2\text{Area} \approx 131.2 \, \text{cm}^2

Answer: The area of the parallelogram is 131 cm² (to 3 significant figures).


(b) Work out the length of diagonal EGEG:

The formula for the diagonal of a parallelogram is derived using the law of cosines:
c2=a2+b22abcos(θ)c^2 = a^2 + b^2 - 2ab\cos(\theta)
where:

  • a=9.3cma = 9.3 \, \text{cm},
  • b=14.7cmb = 14.7 \, \text{cm},
  • θ=106\theta = 106^\circ.

First, calculate cos(106)\cos(106^\circ):
cos(106)0.2756\cos(106^\circ) \approx -0.2756.

Now substitute into the formula:
EG2=9.32+14.722(9.3)(14.7)(0.2756)EG^2 = 9.3^2 + 14.7^2 - 2(9.3)(14.7)(-0.2756)
EG2=86.49+216.09+75.595EG^2 = 86.49 + 216.09 + 75.595
EG2378.175EG^2 \approx 378.175
EG378.17519.4cmEG \approx \sqrt{378.175} \approx 19.4 \, \text{cm}

Answer: The length of diagonal EGEG is 19.4 cm (to 3 significant figures).


Would you like a step-by-step breakdown of any part of this solution?

Related Questions:

  1. What is the formula for calculating the sine of an angle?
  2. How does the law of cosines apply to non-right triangles?
  3. Can we calculate the area using a different method (e.g., without trigonometry)?
  4. What is the significance of rounding to 3 significant figures?
  5. How does the cosine of an obtuse angle differ from an acute angle?

Tip: Always keep your calculator in degree mode unless working in radians!

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Math Problem Analysis

Mathematical Concepts

Geometry
Trigonometry
Parallelograms

Formulas

Area of parallelogram = a * b * sin(θ)
Law of Cosines: c² = a² + b² - 2ab * cos(θ)

Theorems

Law of Sines
Law of Cosines

Suitable Grade Level

Grades 9-12