We are given a right triangle $LMN$ with $|LM| = 6$ cm, $\angle LMN = 90^\circ$, $\angle LNM = x$, and $\sin x = \frac{3}{5}$. We want to find the area of triangle $LMN$.

GeometryTrigonometryRight TriangleAreaSineTangentPythagorean Theorem
2025/4/11

1. Problem Description

We are given a right triangle LMNLMN with LM=6|LM| = 6 cm, LMN=90\angle LMN = 90^\circ, LNM=x\angle LNM = x, and sinx=35\sin x = \frac{3}{5}. We want to find the area of triangle LMNLMN.

2. Solution Steps

Since sinx=35\sin x = \frac{3}{5}, we can form a right triangle with opposite side 3 and hypotenuse

5. Using the Pythagorean theorem, the adjacent side is $\sqrt{5^2 - 3^2} = \sqrt{25 - 9} = \sqrt{16} = 4$.

Then cosx=45\cos x = \frac{4}{5} and tanx=34\tan x = \frac{3}{4}.
In triangle LMNLMN, we have LMN=90\angle LMN = 90^\circ. Also, LM=6|LM| = 6 cm. Since LNM=x\angle LNM = x, we can write
tanx=LMMN=6MN\tan x = \frac{LM}{MN} = \frac{6}{MN}.
We are given that sinx=35\sin x = \frac{3}{5}, so tanx=34\tan x = \frac{3}{4}. Therefore, we have
6MN=34\frac{6}{MN} = \frac{3}{4}
MN=6×43=243=8MN = \frac{6 \times 4}{3} = \frac{24}{3} = 8 cm.
The area of triangle LMNLMN is
Area =12×LM×MN=12×6×8=482=24= \frac{1}{2} \times LM \times MN = \frac{1}{2} \times 6 \times 8 = \frac{48}{2} = 24 cm2^2.

3. Final Answer

C. 24 cm2^2

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