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In a triangle ABC, side a = 6.7 cm, side c = 2.3 cm and angle B = 46.6 degrees. Find side b and angle A.

Mathematics

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Answer

5.39 cm5.39 \text{ cm}

64.7∘64.7^\circ

68.7∘68.7^\circ

Step-by-step solution

3 steps
  1. Find side bb using the Cosine Rule.

    The Cosine Rule states b2=a2+c2−2accos⁡Bb^2 = a^2 + c^2 - 2ac \cos B.
    Given a=6.7 cma = 6.7 \text{ cm}, c=2.3 cmc = 2.3 \text{ cm}, and B=46.6∘B = 46.6^\circ.

    Substitute the values into the formula:

    b2=(6.7)2+(2.3)2−2(6.7)(2.3)cos⁡(46.6∘)b^2 = (6.7)^2 + (2.3)^2 - 2(6.7)(2.3) \cos(46.6^\circ)

    Calculate the squares:

    b2=44.89+5.29−2(6.7)(2.3)cos⁡(46.6∘)b^2 = 44.89 + 5.29 - 2(6.7)(2.3) \cos(46.6^\circ)

    Sum the squared terms:

    b2=50.18−2(6.7)(2.3)cos⁡(46.6∘)b^2 = 50.18 - 2(6.7)(2.3) \cos(46.6^\circ)

    Multiply the terms in the cosine part:

    b2=50.18−30.82cos⁡(46.6∘)b^2 = 50.18 - 30.82 \cos(46.6^\circ)

    Calculate cos⁡(46.6∘)\cos(46.6^\circ):

    cos⁡(46.6∘)≈0.687004\cos(46.6^\circ) \approx 0.687004

    Substitute this value:

    b2=50.18−30.82(0.687004)b^2 = 50.18 - 30.82(0.687004) b2=50.18−21.179999999999996b^2 = 50.18 - 21.179999999999996 b2=29.000000000000004b^2 = 29.000000000000004

    Take the square root to find bb:

    b=29.000000000000004b = \sqrt{29.000000000000004} b≈5.38516 cmb \approx 5.38516 \text{ cm}

    Rounding to three significant figures:

    b≈5.39 cmb \approx 5.39 \text{ cm}
  2. Find angle AA using the Sine Rule.

    The Sine Rule states asin⁡A=bsin⁡B\frac{a}{\sin A} = \frac{b}{\sin B}.
    We have a=6.7 cma = 6.7 \text{ cm}, b≈5.38516 cmb \approx 5.38516 \text{ cm}, and B=46.6∘B = 46.6^\circ.

    Rearrange the formula to solve for sin⁡A\sin A:

    sin⁡A=asin⁡Bb\sin A = \frac{a \sin B}{b}

    Substitute the values:

    sin⁡A=6.7sin⁡(46.6∘)5.38516\sin A = \frac{6.7 \sin(46.6^\circ)}{5.38516}

    Calculate sin⁡(46.6∘)\sin(46.6^\circ):

    sin⁡(46.6∘)≈0.726591\sin(46.6^\circ) \approx 0.726591

    Substitute this value:

    sin⁡A=6.7×0.7265915.38516\sin A = \frac{6.7 \times 0.726591}{5.38516} sin⁡A=4.86815975.38516\sin A = \frac{4.8681597}{5.38516} sin⁡A≈0.90400\sin A \approx 0.90400

    Now, find AA by taking the inverse sine:

    A=arcsin⁡(0.90400)A = \arcsin(0.90400) A≈64.690∘A \approx 64.690^\circ

    Rounding to one decimal place:

    A≈64.7∘A \approx 64.7^\circ
  3. Find angle CC using the sum of angles in a triangle.

    The sum of angles in a triangle is 180∘180^\circ.

    A+B+C=180∘A + B + C = 180^\circ

    We have A≈64.690∘A \approx 64.690^\circ and B=46.6∘B = 46.6^\circ.

    Rearrange to solve for CC:

    C=180∘−A−BC = 180^\circ - A - B

    Substitute the values:

    C=180∘−64.690∘−46.6∘C = 180^\circ - 64.690^\circ - 46.6^\circ C=180∘−111.290∘C = 180^\circ - 111.290^\circ C=68.710∘C = 68.710^\circ

    Rounding to one decimal place:

    C≈68.7∘C \approx 68.7^\circ

    The final answers are:

    b≈5.39 cmb \approx \boxed{5.39 \text{ cm}} A≈64.7∘A \approx \boxed{64.7^\circ} C≈68.7∘C \approx \boxed{68.7^\circ}
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