The problem consists of two parts. (2) In triangle ABC, we are given angle $A = 125.4^{\circ}$, side $b = 29.4$ cm, and side $c = 5$ cm. We need to find the length of side $a$. (3) In triangle ABC, we are given angle $C = 47.8^{\circ}$, side $a = 13.1$ m, and side $b = 24.2$ m. We need to find the length of side $c$.

GeometryLaw of CosinesTrianglesTrigonometryTriangle Sides and Angles
2025/3/18

1. Problem Description

The problem consists of two parts.
(2) In triangle ABC, we are given angle A=125.4A = 125.4^{\circ}, side b=29.4b = 29.4 cm, and side c=5c = 5 cm. We need to find the length of side aa.
(3) In triangle ABC, we are given angle C=47.8C = 47.8^{\circ}, side a=13.1a = 13.1 m, and side b=24.2b = 24.2 m. We need to find the length of side cc.

2. Solution Steps

(2) We can use the Law of Cosines to find side aa. The Law of Cosines states:
a2=b2+c22bccosAa^2 = b^2 + c^2 - 2bc \cos{A}
Plugging in the given values:
a2=(29.4)2+(5)22(29.4)(5)cos(125.4)a^2 = (29.4)^2 + (5)^2 - 2(29.4)(5) \cos{(125.4^{\circ})}
a2=864.36+25294cos(125.4)a^2 = 864.36 + 25 - 294 \cos{(125.4^{\circ})}
a2=889.36294(0.5787)a^2 = 889.36 - 294(-0.5787)
a2=889.36+170.13a^2 = 889.36 + 170.13
a2=1059.49a^2 = 1059.49
a=1059.49a = \sqrt{1059.49}
a32.55a \approx 32.55 cm
(3) We can use the Law of Cosines to find side cc. The Law of Cosines states:
c2=a2+b22abcosCc^2 = a^2 + b^2 - 2ab \cos{C}
Plugging in the given values:
c2=(13.1)2+(24.2)22(13.1)(24.2)cos(47.8)c^2 = (13.1)^2 + (24.2)^2 - 2(13.1)(24.2) \cos{(47.8^{\circ})}
c2=171.61+585.64634.84cos(47.8)c^2 = 171.61 + 585.64 - 634.84 \cos{(47.8^{\circ})}
c2=757.25634.84(0.6713)c^2 = 757.25 - 634.84(0.6713)
c2=757.25425.15c^2 = 757.25 - 425.15
c2=332.10c^2 = 332.10
c=332.10c = \sqrt{332.10}
c18.22c \approx 18.22 m

3. Final Answer

(2) a32.55a \approx 32.55 cm
(3) c18.22c \approx 18.22 m

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