In triangle $ABC$, we are given side $b = 14.35$ cm, side $a = 7.82$ cm, and angle $B = 115^{\circ}$. We need to solve the triangle completely, meaning we need to find the remaining angle $A$ and $C$, and the remaining side $c$.

GeometryTriangleLaw of SinesTrigonometryTriangle Solution
2025/3/12

1. Problem Description

In triangle ABCABC, we are given side b=14.35b = 14.35 cm, side a=7.82a = 7.82 cm, and angle B=115B = 115^{\circ}. We need to solve the triangle completely, meaning we need to find the remaining angle AA and CC, and the remaining side cc.

2. Solution Steps

First, we use the Law of Sines to find angle AA.
asinA=bsinB\frac{a}{\sin A} = \frac{b}{\sin B}
sinA=asinBb\sin A = \frac{a \sin B}{b}
A=arcsin(asinBb)A = \arcsin(\frac{a \sin B}{b})
A=arcsin(7.82sin(115)14.35)A = \arcsin(\frac{7.82 \sin(115^{\circ})}{14.35})
A=arcsin(7.82×0.906314.35)A = \arcsin(\frac{7.82 \times 0.9063}{14.35})
A=arcsin(7.08814.35)A = \arcsin(\frac{7.088}{14.35})
A=arcsin(0.494)A = \arcsin(0.494)
A=29.60A = 29.60^{\circ}
Next, we can calculate angle CC using the fact that the sum of angles in a triangle is 180180^{\circ}.
A+B+C=180A + B + C = 180^{\circ}
C=180ABC = 180^{\circ} - A - B
C=18029.60115C = 180^{\circ} - 29.60^{\circ} - 115^{\circ}
C=35.40C = 35.40^{\circ}
Finally, we can find side cc using the Law of Sines.
csinC=bsinB\frac{c}{\sin C} = \frac{b}{\sin B}
c=bsinCsinBc = \frac{b \sin C}{\sin B}
c=14.35sin(35.40)sin(115)c = \frac{14.35 \sin(35.40^{\circ})}{\sin(115^{\circ})}
c=14.35×0.57930.9063c = \frac{14.35 \times 0.5793}{0.9063}
c=8.3130.9063c = \frac{8.313}{0.9063}
c=9.17 cmc = 9.17 \text{ cm}

3. Final Answer

A=29.60A = 29.60^{\circ}
C=35.40C = 35.40^{\circ}
c=9.17 cmc = 9.17 \text{ cm}

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